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deleted 8 characters in body

edited Jul 2, 2017 at 22:40

Uses smls's idea of squishing the maze to make each cell 1x1 and removing double directionsrepeated arrows from the final output.

added 13 characters in body

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edited Jul 2, 2017 at 21:55

Justin Mariner

JavaScript (ES6), 366356 bytes

a=>(a=a.map(s=>s.filter((_,i)=>!i|i%3)),g=([x,y])=>a[y]&&a[y][x],o=[],c=([x,y],m="",v=[])=>[[0,1],[1,0],[0,-1],[-1,0]].map(([j,k],i)=>(p=[x+j,y+k],!m&(!y|y>a[l="length"]-2)==i%2|v.includes(""+p)||(g(p)<"!"?c(p,m+"v>^<"[i],[...v,""+p]):g(p)=="U"?o.push(m.replace(/(.)\1/g,"$1")):0))),a.map((h,i)=>h.map((k,j)=>k=="I"&&c([j,i]))),o.map(m=>m.replace(/(.)\1/g,"$1")).sort((a,b)=>a[l]-b[l])[0])

a=>( a=a.map(s=>s.filter((_,i)=>!i|i%3)), // squish the maze to 1x1 cells g=([x,y])=>a[y]&&a[y][x], // helper func to get maze value o=[], // resulting movesets c=([x,y], m="", v=[]) => // recursive func to search // takes current point, moves, and visited spots [[0,1],[1,0],[0,-1],[-1,0]].map(([j,k],i)=>(// for each direction p=[x+j,y+k], !m & (!y | y>a[l="length"]-2) == i%2 | // if first move, prevent moving out of maze v.includes(""+p) || ( // also prevent if already visited g(p)<"!" ? // is this a space? c(p, m+"v>^<"[i], [...v,""+p]) // check this spot recursively : g(p)=="U" ? // if this the end? o.push(m)  // add moves to moveset   m.replace(/(.)\1/g,"$1")) // with double arrows removed  : 0 ) )), a.map((h,i)=>h.map((k,j)=> // find the starting "I" and k=="I" && c([j,i]) // begin recursion at that point )), o.map(m=>m.replace(/(.)\1/g,"$1")) // remove doubled directions .sort((a,b)=>a[l]-b[l])[0]  // get shortest path )

f= a=>(a=a.map(s=>s.filter((_,i)=>!i|i%3)),g=([x,y])=>a[y]&&a[y][x],o=[],c=([x,y],m="",v=[])=>[[0,1],[1,0],[0,-1],[-1,0]].map(([j,k],i)=>(p=[x+j,y+k],!m&(!y|y>a[l="length"]-2)==i%2|v.includes(""+p)||(g(p)<"!"?c(p,m+"v>^<"[i],[...v,""+p]):g(p)=="U"?o.push(m):0))),a.map((h,i)=>h.map((k,j)=>k=="I"&&c([j,i]))),o.map(m=>m.replace(/(.)\1/g,"$1")).sort((a,b)=>a[l]-b[l])[0]) let tests = [" +--+--+--+--+--+--+--+--+--+--+\nI | | |\n + +--+--+--+ + + + +--+ +\n | | | | | |\n +--+--+--+ +--+--+ + + +--+\n | | | | |\n + +--+--+ + +--+--+ +--+ +\n | | | | | |\n +--+ + +--+--+ +--+--+ + +\n | | | | | |\n + +--+--+--+ +--+--+ + + +\n | | | | | |\n +--+ + +--+--+ +--+--+--+--+\n | | | | |\n + + +--+--+--+ +--+ + + +\n | | | | | | | |\n +--+--+ + +--+ + + +--+ +\n | | | | | |\n + +--+--+--+ + + + + +--+\n | | | | U\n +--+--+--+--+--+--+--+--+--+--+"," +--+--+--+--+--+\nI | | |\n + +--+--+ + +\n | | | |\n + +--+ + + +\n | | | | |\n + + +--+ + +\n | | |\n +--+ + +--+--+\n | | U\n +--+--+--+--+--+"," +--+--+--+--+--+\nU | |\n + + +--+--+ +\n | | | |\n +--+--+ + +--+\n | | |\n + +--+--+--+ +\n | | | |\n + + + + +--+\n | | I\n +--+--+--+--+--+"," +--+--+--+--+--+\nU | |\n + + +--+--+ +\n | | |\n +--+--+ + +--+\n | | |\n + +--+--+--+ +\n | | | |\n + + + + +--+\n | | I\n +--+--+--+--+--+"," I\n +--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+\n | | | | |\n + + + +--+--+--+ + +--+--+ +--+--+ + +\n | | | | | | | |\n +--+--+--+ +--+ + +--+--+--+--+ +--+--+--+\n | | | | | | | | |\n + + + + + +--+ + + + +--+--+ +--+ +\n | | | | | | | |\n + +--+--+--+ +--+--+ + +--+ +--+--+ +--+\n | | | | | | | | |\n + +--+ + +--+ +--+--+ +--+--+ + +--+ +\n | | | | | | |\n + + +--+--+--+--+ + +--+--+--+ +--+ +--+\n | | | | | | | |\n +--+--+--+ + +--+--+ +--+ + +--+ +--+ +\n | | | | | | | |\n + +--+--+--+--+ + + +--+--+--+ + + + +\n | | | | | | | | | |\n +--+ + + + + + +--+--+ + + +--+ + +\n | | | | | | | | | |\n +--+ +--+--+ + + + +--+--+--+ + + + +\n | | | | | | | | | |\n + +--+ +--+--+ + +--+--+ + +--+ + + +\n | | | | | | | | | |\n +--+--+--+ + + +--+ + +--+--+ +--+ + +\n | | | | | | | |\n + + +--+--+--+--+ +--+--+ +--+--+ +--+ +\n | | | | | |\n + + + +--+--+--+--+--+--+--+--+ +--+ +--+\n | | | |\n +--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+\n U"," +--+--+--+--+--+\nI |\n + + + + + +\n | |\n + + + + + +\n | |\n + + + + + +\n | |\n + + + + + +\n | U\n +--+--+--+--+--+"," I U\n + + +--+--+--+\n | | | |\n + +--+--+ + +\n | | | |\n +--+ + +--+ +\n | | | |\n + +--+ + + +\n | | |\n +--+ +--+--+ +\n | | |\n +--+--+--+--+--+"," +--+--+--+--+--+\n | | |\n + +--+ +--+ +\nI | | | |\n + + +--+ + +\nU | | | |\n +--+--+ + + +\n | | | |\n + +--+--+--+ +\n | \n +--+--+--+--+--+"]; S.innerHTML="<option>Tests"+Array(tests.length-1).fill().map((_,i)=>"<option>"+(i+1)).join``;

<select id=S oninput="I.value=S.selectedIndex?tests[S.value]:''"></select><br> <textarea id=I rows=20 cols=50></textarea><br><button onclick="O.innerHTML=f(I.value.split`\n`.map(x=>[...x]))">Run</button> <pre id=O>

f= a=>(a=a.map(s=>s.filter((_,i)=>!i|i%3)),g=([x,y])=>a[y]&&a[y][x],o=[],c=([x,y],m="",v=[])=>[[0,1],[1,0],[0,-1],[-1,0]].map(([j,k],i)=>(p=[x+j,y+k],!m&(!y|y>a[l="length"]-2)==i%2|v.includes(""+p)||(g(p)<"!"?c(p,m+"v>^<"[i],[...v,""+p]):g(p)=="U"?o.push(m.replace(/(.)\1/g,"$1")):0))),a.map((h,i)=>h.map((k,j)=>k=="I"&&c([j,i]))),o.sort((a,b)=>a[l]-b[l])[0]) let tests = [" +--+--+--+--+--+--+--+--+--+--+\nI | | |\n + +--+--+--+ + + + +--+ +\n | | | | | |\n +--+--+--+ +--+--+ + + +--+\n | | | | |\n + +--+--+ + +--+--+ +--+ +\n | | | | | |\n +--+ + +--+--+ +--+--+ + +\n | | | | | |\n + +--+--+--+ +--+--+ + + +\n | | | | | |\n +--+ + +--+--+ +--+--+--+--+\n | | | | |\n + + +--+--+--+ +--+ + + +\n | | | | | | | |\n +--+--+ + +--+ + + +--+ +\n | | | | | |\n + +--+--+--+ + + + + +--+\n | | | | U\n +--+--+--+--+--+--+--+--+--+--+"," +--+--+--+--+--+\nI | | |\n + +--+--+ + +\n | | | |\n + +--+ + + +\n | | | | |\n + + +--+ + +\n | | |\n +--+ + +--+--+\n | | U\n +--+--+--+--+--+"," +--+--+--+--+--+\nU | |\n + + +--+--+ +\n | | | |\n +--+--+ + +--+\n | | |\n + +--+--+--+ +\n | | | |\n + + + + +--+\n | | I\n +--+--+--+--+--+"," +--+--+--+--+--+\nU | |\n + + +--+--+ +\n | | |\n +--+--+ + +--+\n | | |\n + +--+--+--+ +\n | | | |\n + + + + +--+\n | | I\n +--+--+--+--+--+"," I\n +--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+\n | | | | |\n + + + +--+--+--+ + +--+--+ +--+--+ + +\n | | | | | | | |\n +--+--+--+ +--+ + +--+--+--+--+ +--+--+--+\n | | | | | | | | |\n + + + + + +--+ + + + +--+--+ +--+ +\n | | | | | | | |\n + +--+--+--+ +--+--+ + +--+ +--+--+ +--+\n | | | | | | | | |\n + +--+ + +--+ +--+--+ +--+--+ + +--+ +\n | | | | | | |\n + + +--+--+--+--+ + +--+--+--+ +--+ +--+\n | | | | | | | |\n +--+--+--+ + +--+--+ +--+ + +--+ +--+ +\n | | | | | | | |\n + +--+--+--+--+ + + +--+--+--+ + + + +\n | | | | | | | | | |\n +--+ + + + + + +--+--+ + + +--+ + +\n | | | | | | | | | |\n +--+ +--+--+ + + + +--+--+--+ + + + +\n | | | | | | | | | |\n + +--+ +--+--+ + +--+--+ + +--+ + + +\n | | | | | | | | | |\n +--+--+--+ + + +--+ + +--+--+ +--+ + +\n | | | | | | | |\n + + +--+--+--+--+ +--+--+ +--+--+ +--+ +\n | | | | | |\n + + + +--+--+--+--+--+--+--+--+ +--+ +--+\n | | | |\n +--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+\n U"," +--+--+--+--+--+\nI |\n + + + + + +\n | |\n + + + + + +\n | |\n + + + + + +\n | |\n + + + + + +\n | U\n +--+--+--+--+--+"," I U\n + + +--+--+--+\n | | | |\n + +--+--+ + +\n | | | |\n +--+ + +--+ +\n | | | |\n + +--+ + + +\n | | |\n +--+ +--+--+ +\n | | |\n +--+--+--+--+--+"," +--+--+--+--+--+\n | | |\n + +--+ +--+ +\nI | | | |\n + + +--+ + +\nU | | | |\n +--+--+ + + +\n | | | |\n + +--+--+--+ +\n | \n +--+--+--+--+--+"]; S.innerHTML="<option>Tests"+Array(tests.length).fill().map((_,i)=>"<option>"+(i+1)).join``;

<select id=S oninput="I.value=S.selectedIndex?tests[S.value-1]:''"></select><br> <textarea id=I rows=20 cols=50></textarea><br><button onclick="O.innerHTML=f(I.value.split`\n`.map(x=>[...x]))">Run</button> <pre id=O>

JavaScript (ES6), 366 bytes

a=>(a=a.map(s=>s.filter((_,i)=>!i|i%3)),g=([x,y])=>a[y]&&a[y][x],o=[],c=([x,y],m="",v=[])=>[[0,1],[1,0],[0,-1],[-1,0]].map(([j,k],i)=>(p=[x+j,y+k],!m&(!y|y>a[l="length"]-2)==i%2|v.includes(""+p)||(g(p)<"!"?c(p,m+"v>^<"[i],[...v,""+p]):g(p)=="U"?o.push(m):0))),a.map((h,i)=>h.map((k,j)=>k=="I"&&c([j,i]))),o.map(m=>m.replace(/(.)\1/g,"$1")).sort((a,b)=>a[l]-b[l])[0])

a=>( a=a.map(s=>s.filter((_,i)=>!i|i%3)), // squish the maze to 1x1 cells g=([x,y])=>a[y]&&a[y][x], // helper func to get maze value o=[], // resulting movesets c=([x,y], m="", v=[]) => // recursive func to search // takes current point, moves, and visited spots [[0,1],[1,0],[0,-1],[-1,0]].map(([j,k],i)=>(// for each direction p=[x+j,y+k], !m & (!y | y>a[l="length"]-2) == i%2 | // if first move, prevent moving out of maze v.includes(""+p) || ( // also prevent if already visited g(p)<"!" ? // is this a space? c(p, m+"v>^<"[i], [...v,""+p]) // check this spot recursively : g(p)=="U" ? // if this the end? o.push(m) // add moves to moveset : 0 ) )), a.map((h,i)=>h.map((k,j)=> // find the starting "I" and k=="I" && c([j,i]) // begin recursion at that point )), o.map(m=>m.replace(/(.)\1/g,"$1")) // remove doubled directions .sort((a,b)=>a[l]-b[l])[0]  // get shortest path )

f= a=>(a=a.map(s=>s.filter((_,i)=>!i|i%3)),g=([x,y])=>a[y]&&a[y][x],o=[],c=([x,y],m="",v=[])=>[[0,1],[1,0],[0,-1],[-1,0]].map(([j,k],i)=>(p=[x+j,y+k],!m&(!y|y>a[l="length"]-2)==i%2|v.includes(""+p)||(g(p)<"!"?c(p,m+"v>^<"[i],[...v,""+p]):g(p)=="U"?o.push(m):0))),a.map((h,i)=>h.map((k,j)=>k=="I"&&c([j,i]))),o.map(m=>m.replace(/(.)\1/g,"$1")).sort((a,b)=>a[l]-b[l])[0]) let tests = [" +--+--+--+--+--+--+--+--+--+--+\nI | | |\n + +--+--+--+ + + + +--+ +\n | | | | | |\n +--+--+--+ +--+--+ + + +--+\n | | | | |\n + +--+--+ + +--+--+ +--+ +\n | | | | | |\n +--+ + +--+--+ +--+--+ + +\n | | | | | |\n + +--+--+--+ +--+--+ + + +\n | | | | | |\n +--+ + +--+--+ +--+--+--+--+\n | | | | |\n + + +--+--+--+ +--+ + + +\n | | | | | | | |\n +--+--+ + +--+ + + +--+ +\n | | | | | |\n + +--+--+--+ + + + + +--+\n | | | | U\n +--+--+--+--+--+--+--+--+--+--+"," +--+--+--+--+--+\nI | | |\n + +--+--+ + +\n | | | |\n + +--+ + + +\n | | | | |\n + + +--+ + +\n | | |\n +--+ + +--+--+\n | | U\n +--+--+--+--+--+"," +--+--+--+--+--+\nU | |\n + + +--+--+ +\n | | | |\n +--+--+ + +--+\n | | |\n + +--+--+--+ +\n | | | |\n + + + + +--+\n | | I\n +--+--+--+--+--+"," +--+--+--+--+--+\nU | |\n + + +--+--+ +\n | | |\n +--+--+ + +--+\n | | |\n + +--+--+--+ +\n | | | |\n + + + + +--+\n | | I\n +--+--+--+--+--+"," I\n +--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+\n | | | | |\n + + + +--+--+--+ + +--+--+ +--+--+ + +\n | | | | | | | |\n +--+--+--+ +--+ + +--+--+--+--+ +--+--+--+\n | | | | | | | | |\n + + + + + +--+ + + + +--+--+ +--+ +\n | | | | | | | |\n + +--+--+--+ +--+--+ + +--+ +--+--+ +--+\n | | | | | | | | |\n + +--+ + +--+ +--+--+ +--+--+ + +--+ +\n | | | | | | |\n + + +--+--+--+--+ + +--+--+--+ +--+ +--+\n | | | | | | | |\n +--+--+--+ + +--+--+ +--+ + +--+ +--+ +\n | | | | | | | |\n + +--+--+--+--+ + + +--+--+--+ + + + +\n | | | | | | | | | |\n +--+ + + + + + +--+--+ + + +--+ + +\n | | | | | | | | | |\n +--+ +--+--+ + + + +--+--+--+ + + + +\n | | | | | | | | | |\n + +--+ +--+--+ + +--+--+ + +--+ + + +\n | | | | | | | | | |\n +--+--+--+ + + +--+ + +--+--+ +--+ + +\n | | | | | | | |\n + + +--+--+--+--+ +--+--+ +--+--+ +--+ +\n | | | | | |\n + + + +--+--+--+--+--+--+--+--+ +--+ +--+\n | | | |\n +--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+\n U"," +--+--+--+--+--+\nI |\n + + + + + +\n | |\n + + + + + +\n | |\n + + + + + +\n | |\n + + + + + +\n | U\n +--+--+--+--+--+"," I U\n + + +--+--+--+\n | | | |\n + +--+--+ + +\n | | | |\n +--+ + +--+ +\n | | | |\n + +--+ + + +\n | | |\n +--+ +--+--+ +\n | | |\n +--+--+--+--+--+"," +--+--+--+--+--+\n | | |\n + +--+ +--+ +\nI | | | |\n + + +--+ + +\nU | | | |\n +--+--+ + + +\n | | | |\n + +--+--+--+ +\n | \n +--+--+--+--+--+"]; S.innerHTML="<option>Tests"+Array(tests.length-1).fill().map((_,i)=>"<option>"+(i+1)).join``;

<select id=S oninput="I.value=S.selectedIndex?tests[S.value]:''"></select><br> <textarea id=I rows=20 cols=50></textarea><br><button onclick="O.innerHTML=f(I.value.split`\n`.map(x=>[...x]))">Run</button> <pre id=O>

JavaScript (ES6), 356 bytes

a=>(a=a.map(s=>s.filter((_,i)=>!i|i%3)),g=([x,y])=>a[y]&&a[y][x],o=[],c=([x,y],m="",v=[])=>[[0,1],[1,0],[0,-1],[-1,0]].map(([j,k],i)=>(p=[x+j,y+k],!m&(!y|y>a[l="length"]-2)==i%2|v.includes(""+p)||(g(p)<"!"?c(p,m+"v>^<"[i],[...v,""+p]):g(p)=="U"?o.push(m.replace(/(.)\1/g,"$1")):0))),a.map((h,i)=>h.map((k,j)=>k=="I"&&c([j,i]))),o.sort((a,b)=>a[l]-b[l])[0])

a=>( a=a.map(s=>s.filter((_,i)=>!i|i%3)), // squish the maze to 1x1 cells g=([x,y])=>a[y]&&a[y][x], // helper func to get maze value o=[], // resulting movesets c=([x,y], m="", v=[]) => // recursive func to search // takes current point, moves, and visited spots [[0,1],[1,0],[0,-1],[-1,0]].map(([j,k],i)=>(// for each direction p=[x+j,y+k], !m & (!y | y>a[l="length"]-2) == i%2 | // if first move, prevent moving out of maze v.includes(""+p) || ( // also prevent if already visited g(p)<"!" ? // is this a space? c(p, m+"v>^<"[i], [...v,""+p]) // check this spot recursively : g(p)=="U" ? // if this the end? o.push(  // add moves to moveset   m.replace(/(.)\1/g,"$1")) // with double arrows removed  : 0 ) )), a.map((h,i)=>h.map((k,j)=> // find the starting "I" and k=="I" && c([j,i]) // begin recursion at that point )), o.sort((a,b)=>a[l]-b[l])[0] // get shortest path )

f= a=>(a=a.map(s=>s.filter((_,i)=>!i|i%3)),g=([x,y])=>a[y]&&a[y][x],o=[],c=([x,y],m="",v=[])=>[[0,1],[1,0],[0,-1],[-1,0]].map(([j,k],i)=>(p=[x+j,y+k],!m&(!y|y>a[l="length"]-2)==i%2|v.includes(""+p)||(g(p)<"!"?c(p,m+"v>^<"[i],[...v,""+p]):g(p)=="U"?o.push(m.replace(/(.)\1/g,"$1")):0))),a.map((h,i)=>h.map((k,j)=>k=="I"&&c([j,i]))),o.sort((a,b)=>a[l]-b[l])[0]) let tests = [" +--+--+--+--+--+--+--+--+--+--+\nI | | |\n + +--+--+--+ + + + +--+ +\n | | | | | |\n +--+--+--+ +--+--+ + + +--+\n | | | | |\n + +--+--+ + +--+--+ +--+ +\n | | | | | |\n +--+ + +--+--+ +--+--+ + +\n | | | | | |\n + +--+--+--+ +--+--+ + + +\n | | | | | |\n +--+ + +--+--+ +--+--+--+--+\n | | | | |\n + + +--+--+--+ +--+ + + +\n | | | | | | | |\n +--+--+ + +--+ + + +--+ +\n | | | | | |\n + +--+--+--+ + + + + +--+\n | | | | U\n +--+--+--+--+--+--+--+--+--+--+"," +--+--+--+--+--+\nI | | |\n + +--+--+ + +\n | | | |\n + +--+ + + +\n | | | | |\n + + +--+ + +\n | | |\n +--+ + +--+--+\n | | U\n +--+--+--+--+--+"," +--+--+--+--+--+\nU | |\n + + +--+--+ +\n | | | |\n +--+--+ + +--+\n | | |\n + +--+--+--+ +\n | | | |\n + + + + +--+\n | | I\n +--+--+--+--+--+"," +--+--+--+--+--+\nU | |\n + + +--+--+ +\n | | |\n +--+--+ + +--+\n | | |\n + +--+--+--+ +\n | | | |\n + + + + +--+\n | | I\n +--+--+--+--+--+"," I\n +--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+\n | | | | |\n + + + +--+--+--+ + +--+--+ +--+--+ + +\n | | | | | | | |\n +--+--+--+ +--+ + +--+--+--+--+ +--+--+--+\n | | | | | | | | |\n + + + + + +--+ + + + +--+--+ +--+ +\n | | | | | | | |\n + +--+--+--+ +--+--+ + +--+ +--+--+ +--+\n | | | | | | | | |\n + +--+ + +--+ +--+--+ +--+--+ + +--+ +\n | | | | | | |\n + + +--+--+--+--+ + +--+--+--+ +--+ +--+\n | | | | | | | |\n +--+--+--+ + +--+--+ +--+ + +--+ +--+ +\n | | | | | | | |\n + +--+--+--+--+ + + +--+--+--+ + + + +\n | | | | | | | | | |\n +--+ + + + + + +--+--+ + + +--+ + +\n | | | | | | | | | |\n +--+ +--+--+ + + + +--+--+--+ + + + +\n | | | | | | | | | |\n + +--+ +--+--+ + +--+--+ + +--+ + + +\n | | | | | | | | | |\n +--+--+--+ + + +--+ + +--+--+ +--+ + +\n | | | | | | | |\n + + +--+--+--+--+ +--+--+ +--+--+ +--+ +\n | | | | | |\n + + + +--+--+--+--+--+--+--+--+ +--+ +--+\n | | | |\n +--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+\n U"," +--+--+--+--+--+\nI |\n + + + + + +\n | |\n + + + + + +\n | |\n + + + + + +\n | |\n + + + + + +\n | U\n +--+--+--+--+--+"," I U\n + + +--+--+--+\n | | | |\n + +--+--+ + +\n | | | |\n +--+ + +--+ +\n | | | |\n + +--+ + + +\n | | |\n +--+ +--+--+ +\n | | |\n +--+--+--+--+--+"," +--+--+--+--+--+\n | | |\n + +--+ +--+ +\nI | | | |\n + + +--+ + +\nU | | | |\n +--+--+ + + +\n | | | |\n + +--+--+--+ +\n | \n +--+--+--+--+--+"]; S.innerHTML="<option>Tests"+Array(tests.length).fill().map((_,i)=>"<option>"+(i+1)).join``;

<select id=S oninput="I.value=S.selectedIndex?tests[S.value-1]:''"></select><br> <textarea id=I rows=20 cols=50></textarea><br><button onclick="O.innerHTML=f(I.value.split`\n`.map(x=>[...x]))">Run</button> <pre id=O>

Source Link

answered Jul 2, 2017 at 21:49

Justin Mariner

JavaScript (ES6), 366 bytes

a=>(a=a.map(s=>s.filter((_,i)=>!i|i%3)),g=([x,y])=>a[y]&&a[y][x],o=[],c=([x,y],m="",v=[])=>[[0,1],[1,0],[0,-1],[-1,0]].map(([j,k],i)=>(p=[x+j,y+k],!m&(!y|y>a[l="length"]-2)==i%2|v.includes(""+p)||(g(p)<"!"?c(p,m+"v>^<"[i],[...v,""+p]):g(p)=="U"?o.push(m):0))),a.map((h,i)=>h.map((k,j)=>k=="I"&&c([j,i]))),o.map(m=>m.replace(/(.)\1/g,"$1")).sort((a,b)=>a[l]-b[l])[0])

Takes input as a 2D array of characters. Each line must be left-padded by one space and have no trailing space, no matter where the start/end points are.

Uses smls's idea of squishing the maze to make each cell 1x1 and removing double directions from the final output.

Ungolfed and Explained

a=>( a=a.map(s=>s.filter((_,i)=>!i|i%3)), // squish the maze to 1x1 cells g=([x,y])=>a[y]&&a[y][x], // helper func to get maze value o=[], // resulting movesets c=([x,y], m="", v=[]) => // recursive func to search // takes current point, moves, and visited spots [[0,1],[1,0],[0,-1],[-1,0]].map(([j,k],i)=>(// for each direction p=[x+j,y+k], !m & (!y | y>a[l="length"]-2) == i%2 | // if first move, prevent moving out of maze v.includes(""+p) || ( // also prevent if already visited g(p)<"!" ? // is this a space? c(p, m+"v>^<"[i], [...v,""+p]) // check this spot recursively : g(p)=="U" ? // if this the end? o.push(m) // add moves to moveset : 0 ) )), a.map((h,i)=>h.map((k,j)=> // find the starting "I" and k=="I" && c([j,i]) // begin recursion at that point )), o.map(m=>m.replace(/(.)\1/g,"$1")) // remove doubled directions .sort((a,b)=>a[l]-b[l])[0] // get shortest path )

Test Snippet

f= a=>(a=a.map(s=>s.filter((_,i)=>!i|i%3)),g=([x,y])=>a[y]&&a[y][x],o=[],c=([x,y],m="",v=[])=>[[0,1],[1,0],[0,-1],[-1,0]].map(([j,k],i)=>(p=[x+j,y+k],!m&(!y|y>a[l="length"]-2)==i%2|v.includes(""+p)||(g(p)<"!"?c(p,m+"v>^<"[i],[...v,""+p]):g(p)=="U"?o.push(m):0))),a.map((h,i)=>h.map((k,j)=>k=="I"&&c([j,i]))),o.map(m=>m.replace(/(.)\1/g,"$1")).sort((a,b)=>a[l]-b[l])[0]) let tests = [" +--+--+--+--+--+--+--+--+--+--+\nI | | |\n + +--+--+--+ + + + +--+ +\n | | | | | |\n +--+--+--+ +--+--+ + + +--+\n | | | | |\n + +--+--+ + +--+--+ +--+ +\n | | | | | |\n +--+ + +--+--+ +--+--+ + +\n | | | | | |\n + +--+--+--+ +--+--+ + + +\n | | | | | |\n +--+ + +--+--+ +--+--+--+--+\n | | | | |\n + + +--+--+--+ +--+ + + +\n | | | | | | | |\n +--+--+ + +--+ + + +--+ +\n | | | | | |\n + +--+--+--+ + + + + +--+\n | | | | U\n +--+--+--+--+--+--+--+--+--+--+"," +--+--+--+--+--+\nI | | |\n + +--+--+ + +\n | | | |\n + +--+ + + +\n | | | | |\n + + +--+ + +\n | | |\n +--+ + +--+--+\n | | U\n +--+--+--+--+--+"," +--+--+--+--+--+\nU | |\n + + +--+--+ +\n | | | |\n +--+--+ + +--+\n | | |\n + +--+--+--+ +\n | | | |\n + + + + +--+\n | | I\n +--+--+--+--+--+"," +--+--+--+--+--+\nU | |\n + + +--+--+ +\n | | |\n +--+--+ + +--+\n | | |\n + +--+--+--+ +\n | | | |\n + + + + +--+\n | | I\n +--+--+--+--+--+"," I\n +--+--+--+--+--+--+--+--+--+--+ +--+--+--+--+\n | | | | |\n + + + +--+--+--+ + +--+--+ +--+--+ + +\n | | | | | | | |\n +--+--+--+ +--+ + +--+--+--+--+ +--+--+--+\n | | | | | | | | |\n + + + + + +--+ + + + +--+--+ +--+ +\n | | | | | | | |\n + +--+--+--+ +--+--+ + +--+ +--+--+ +--+\n | | | | | | | | |\n + +--+ + +--+ +--+--+ +--+--+ + +--+ +\n | | | | | | |\n + + +--+--+--+--+ + +--+--+--+ +--+ +--+\n | | | | | | | |\n +--+--+--+ + +--+--+ +--+ + +--+ +--+ +\n | | | | | | | |\n + +--+--+--+--+ + + +--+--+--+ + + + +\n | | | | | | | | | |\n +--+ + + + + + +--+--+ + + +--+ + +\n | | | | | | | | | |\n +--+ +--+--+ + + + +--+--+--+ + + + +\n | | | | | | | | | |\n + +--+ +--+--+ + +--+--+ + +--+ + + +\n | | | | | | | | | |\n +--+--+--+ + + +--+ + +--+--+ +--+ + +\n | | | | | | | |\n + + +--+--+--+--+ +--+--+ +--+--+ +--+ +\n | | | | | |\n + + + +--+--+--+--+--+--+--+--+ +--+ +--+\n | | | |\n +--+--+--+--+--+--+--+--+--+ +--+--+--+--+--+\n U"," +--+--+--+--+--+\nI |\n + + + + + +\n | |\n + + + + + +\n | |\n + + + + + +\n | |\n + + + + + +\n | U\n +--+--+--+--+--+"," I U\n + + +--+--+--+\n | | | |\n + +--+--+ + +\n | | | |\n +--+ + +--+ +\n | | | |\n + +--+ + + +\n | | |\n +--+ +--+--+ +\n | | |\n +--+--+--+--+--+"," +--+--+--+--+--+\n | | |\n + +--+ +--+ +\nI | | | |\n + + +--+ + +\nU | | | |\n +--+--+ + + +\n | | | |\n + +--+--+--+ +\n | \n +--+--+--+--+--+"]; S.innerHTML="<option>Tests"+Array(tests.length-1).fill().map((_,i)=>"<option>"+(i+1)).join``;

<select id=S oninput="I.value=S.selectedIndex?tests[S.value]:''"></select><br> <textarea id=I rows=20 cols=50></textarea><br><button onclick="O.innerHTML=f(I.value.split`\n`.map(x=>[...x]))">Run</button> <pre id=O>