Python 2, 154 bytes

import collections c = collections.Counter() for line in open("input.txt"): c |= collections.Counter(line.upper()) print "".join(sorted(c.elements())) 

C, 298 bytes

char c; int j,n; char C[26]; char D[26]; int main() { char a='a'; while((c=getchar())>=0) { c=tolower(c); if(c>=a&&c<='z'){j=c-a;D[j]++;} if(c=='\n'){ for(j=0;j<26;j++){ if(D[j]>C[j]) {C[j]=D[j];} D[j]=0; } } } for(j=0;j<26;j++) { n=C[j]; while(n--) { putchar(a+j); } } } 

Array D holds tally of letters for each line, then the maximum count is copied to C.

Note: I put my answer yesterday but is now not listed, maybe I pressed delete instead of edit by mistake?

PHP, 143 bytes

Assuming that input is passed in variable $s:

$i=explode("\n",$s);foreach(range('a','z')as$c){$x=array_map(function($l)use($c){return substr_count($l,$c);},$i);echo str_repeat($c,max($x));} 

Explanation

For each possible letter I'm mapping array containing list of strings through a user-defined function which replaces each line with number of characters used. For letter 'd' the line "Mommy loves daddy" will be mapped into 3.

Afterwards I find maximum value inside array and output letter just this many times. Here is multi-line version:

$i=explode("\n",$s); foreach(range('A','Z')as $c){ $x=array_map(function($l)use($c){ return substr_count($l,$c); },$i); echo str_repeat($c,max($x)); } 

Jelly, 7, 6, 5 or 4 bytes

ỴŒuœ|/Ṣ 

Try it online!

Function submission. Depending on how you interpret the I/O rules, it may be possible to drop the leading Ỵ (which would then require input to be the data structure "list of strings", as opposed to a single string that was divided using newlines); and it may be possible to drop the Œu (which would then require the input to use a consistent case for the output to be correct).

Explanation

ỴŒuœ|/Ṣ Ỵ Split on newlines Œu Uppercase each resulting string / Combine the resulting strings using… œ| …multiset union Ṣ Sort 

Julia

78 bytes

it is my 1st approach

!I=join((A='A':'Z').^[max([count(c->c==a,i) for i=split(I,'\n')]...) for a=A])

Attempt This Online!

or

69 66 bytes

• -3 bytes: @MarcMush, thank You
• it is inspired by @Laikoni's Haskell answer

!I=prod(maximum(filter(==(a),i) for i=split(I,' ')) for a='A':'Z')

Attempt This Online!

Python (209, with the sample included, 136 without.):

from collections import*;c=Counter() for i in ["Hello","I love cat", "I love Dog", "I love mommy", "Mommy loves daddy"]: for j in i.lower(): c[j]=max(c[j],list(i).count(j)) print "".join(sorted(c.elements())) 

I'll post a PYG sample this afternoon.

JavaScript, 199 characters

function(n){for(s in p=n.toUpperCase(t=[]).split("\n"))for(i in p[k={},s])t[l=p[s][i]]=Math.max(t[l]||0,k[l]=k[l]+1||1);for(l in t)t.push(new Array(t[l]+1).join(l));return t.sort().join('').trim()} 

C++, 264 characters.

Reads lowercase text from standard input.

#include<algorithm> #include<iostream> #include<map> using namespace std;main(){string s;map<int,long> m;while(getline(cin,s)){int c='`';while(c++<'z')m[c]=max(m[c],count_if(begin(s),end(s),[c](int d){return d==c;}));}for(auto i:m)cout<<string(i.second,i.first);} 

C++ function, 205 characters.

string a(istream&i){string s;map<int,long> m;while(getline(i,s)){int c='`';while(c++<'z')m[c]=max(m[c],count_if(begin(s),end(s),[c](int d){return d==c;}));}for(auto i:m)s.append(i.second,i.first);return s;} 

JavaScript - 244

Accepts a parameter of string with newlines.

function s(z){n=m="",y=[];z.toLowerCase().split("\n").map(function(g){a=[];g.replace(/ /g,n).split(n).map(function(e,i){if((+y[e]|0)<(a[e]=(+a[e]|0)+1))y[e]=a[e];});});for(var b in y){m+=Array(y[b]+1).join(b);}return m.split(n).sort().join(n);} 

Not happy with the sorting and preparation of the output.

Edit: case-insensitive regex unnecessary! Thanks @Bergi

Lua - 206 Chars

g=string f,t,b,e=io.lines(({...})[1]),{},g.byte,g.char for s in f do for c=b"a",b"a" do _,d=s:lower():gsub(e(c),"");t[c]=t[c]and(t[c]>d and t[c])or d end end for c=b"a",b"z" do io.write(g.rep(e(c),t[c]))end 

Reads from the file passed via command line, then creates a table with the maximum number of occurences per letter. Finally outputs the occuring letters.

Java, 335

Here is the executable code in java in a more readable form. Once all the unnecessary white spaces are removed, you will see 335 characters in all. The output is:

ACDDDEGHILLMMMOOSTVYY

It gets a filename as input and reads each character from the file, converts it to uppercase and stores the count of it's occurrence in an array. For every new line, the maximum occurrence of each character is updated. At last it is printed. Pre-requiste: The file should end with a newline.

class F { public static void main(String[] a) throws Exception { java.io.FileInputStream f = new java.io.FileInputStream(a[0]); int j, r, l = 256; int[] i = new int[l], t = new int[l]; while ((r = f.read()) > 0) { r = r > 96 ? r - 32 : r; if (r == 10) for (j = 0; j < l; j++) { i[j] = i[j] < t[j] ? t[j] : i[j]; t[j] = 0; } else t[r]++; } for (j = 65; j < 91; j++) while (i[j]-- > 0) System.out.print((char) j); } } 

After removing the white spaces the code will look like the following:

class F{public static void main(String[] a)throws Exception{java.io.FileInputStream f=new java.io.FileInputStream(a[0]);int j,r,l=256;int[] i=new int[l],t=new int[l];while((r=f.read())>0){r=r>96?r-32:r;if(r==10)for(j=0;j<l;j++){i[j]=i[j]<t[j]?t[j]:i[j];t[j]=0;}else t[r]++;}for(j=65;j<91;j++)while(i[j]-->0)System.out.print((char)j);}} 

C#, 265 characters

Assuming input is in variable s, here's a C# Expression, using mainly LINQ (Enumerable.cs):

string.Join("",s.ToLower().Split('\n').Select(e=>e.Where(l=>l!=' '&&l!='\r') .GroupBy(l=>l).ToDictionary(k=>k.Key,v=>v.Count())).SelectMany(u=>u).GroupBy(l=>l.Key) .Select(g=>new String(Enumerable.Range(1,g.Max(v=>v.Value)).Select(i=>g.Key).ToArray())) .OrderBy(l=>l)) 

C# - 146 Bytes

var x="";foreach(var l in File.ReadAllLines(t))foreach(var p in l)if(x.Count(c=>c==p)<l.Count(c=>c==p))x+=p;string.Concat(x.OrderBy(o=>o)).Trim(); 

Well, I think this is as short as C# can get. This code expects a path to the text file in the variable t.

Japt v1.4.5, 11 bytes

;CËpUmèD rw 

Try it online!

Unpacked & How it works

;CmDEF{DpUmèD rw ; Use an alternative set of predefined variables C "abc...z" mDEF{ Map over each char and form a string... UmèD Map over input array into char count rw Reduce with max Dp Repeat the char this number of times 

Powershell, 118 116 87 bytes

-join($args|%{$_|% t*y|group|%{-join$_.Group}}|sort|group{$_[0]}|%{$_.Group[-1]})|% t*m 

Less golfed test script:

$f = { $x=$args|%{$_|% t*y|group|%{-join$_.Group}} # unsorted groups of the same letters for each sentence: (h,e,ll,o), (...), (...), (i, ,l,oo,v,e,d,g),... $y=$x|sort|group{$_[0]} # sort all groups and group it again by the first letter (( , , , ), (a,a), (c), (d,ddd), ... (y,yy)) $z=$y|%{$_.Group[-1]} # get a last item (maximum item) from each group -join($z)|% t*m # join it and trim spaces } @( ,("acdddeghillmmmoostvyy", "hello", "i love cat", "i love dog", "i love mommy", "mommy loves daddy") ,("AAAAAAAAAAAAAAAABBBCCCCDDDDDEEEEEEEEEFFGGGGHHHHHHIIIIIIIIIIJJKKLLLLMMMMMMMNNNNNNNNNNNNNOOOOOOOOOPPPPPPPQRRRRRRSSSSSSSTTTTTTUUUUUVWWXYYY", "I SAW THE MAN WITH THE BINOCULARS", "THEY ARE HUNTING DOGS", "FREE WHALES", "POLICE HELP DOG BITE VICTIM", "HE SAW THAT GAS CAN EXPLODE", "TURN RIGHT HERE", "WE SAW HER DUCK", "IN ANIMAL CRACKERS GROUCHO MARX AS CAPTAIN RUFUS T SPAULDING QUIPPED ONE MORNING I SHOT AN ELEPHANT IN MY PAJAMAS HOW HE GOT IN MY PAJAMAS I DONT KNOW", "SHIP SAILS TOMORROW", "BOOK STAYS IN LONDON", "WANTED A NURSE FOR A BABY ABOUT TWENTY YEARS OLD", "THE GIRL IN THE CAR THAT NEEDED WATER IS WAITING", "DID YOU EVER HEAR THE STORY ABOUT THE BLIND CARPENTER WHO PICKED UP HIS HAMMER AND SAW", "THOSE PROSECUTORS HAVE BEEN TRYING TO LOCK HIM UP FOR TEN YEARS", "FLYING PLANES CAN BE DANGEROUS", "I ONCE SAW A DEER RIDING MY BICYCLE", "TOILET OUT OF ORDER PLEASE USE FLOOR BELOW", "LOOK AT THE DOG WITH ONE EYE") ) | %{ $expected,$s = $_ $result = &$f @s "$($result-eq$expected): $result" } 

Output:

True: acdddeghillmmmoostvyy True: AAAAAAAAAAAAAAAABBBCCCCDDDDDEEEEEEEEEFFGGGGHHHHHHIIIIIIIIIIJJKKLLLLMMMMMMMNNNNNNNNNNNNNOOOOOOOOOPPPPPPPQRRRRRRSSSSSSSTTTTTTUUUUUVWWXYYY 

Vyxal as, 12 bytes

ȧ∑U:ƛ?vOG;*s 

Try it Online!

 U # Unique characters of... ȧ∑ # The input, with whitespace removed * # Repeated by... :ƛ ; # Themselves mapped to... G # The highest... vO # Amount of... # (implicit) That character ? # In the input s # Sorted. 

Japt -Px, 9 8 bytes

I knew there had to be a way to to it in 8!

cü üÎËÍÌ 

Try it

cü üÎËÍÌ :Implicit input of array c :Flat map ü : Group & sort by value ü :Group & sort by Î : First character Ë :Map Í : Sort Ì : Last element :Implicitly join, trim and output 

Original (w/o flags), 9 bytes

Takes input as an array of lowercase strings.

;C£ËoXÃÍo 

Try it

;C£ËoXÃÍo :Implicit input of array U ;C :Lowercase alphabet £ :Map each X Ë : Map U oX : Remove all characters but X à : End inner map Í : Sort o : Pop last element 

JavaScript (Node.js), 95 bytes

a=>(g=i=>i?g(i-1,i=i.toString(36))+i.repeat(Math.max(...a.map(y=>y.split(i).length))-1):'')(35) 

Try it online!

Thunno 2 J, 7 bytes

ẠıȷcGn× 

Attempt This Online!

Port of Kevin Cruijssen's 05AB1E answer.

Explanation

ẠıȷcGn× # Implicit input Ạı # Map over lowercase alphabet: ȷc # Count in each input string G # Pop and leave the maximum n× # Repeat the character that many times # Implicit output, joined 

AWK, 119 bytes

@load"ordchr" {for(i=0;i++<26;y>a[x]&&a[x]=y)y=gsub(x=chr(i+96),X)}END{for(;j++<26;)for(i=a[x=chr(j+96)];i--;)printf x} 

Attempt This Online!

Assumes lowercase input.

C - 224 bytes or 227 bytes or 228 bytes

(I belive this one breaks the record for C UwU, at the time of writing this there 99 bytes one but it doesn't work)

This assumes that the input has NO same letter with differing casing so "Sentence sentence" (where the 's' has two casing)

// 224 bytes #include <stdio.h> int main(){int b,d,a['{']={};do{int c['{']={};while((b=getchar())!=10&&b!=EOF)c[b]++;for(d='a';d<='z';d++)if(c[d]>a[d])a[d]=c[d];}while(b!=EOF);for(b='a';b<='z';b++)for(d=a[b];d--;putchar(b));putchar(10);} 

This version always lowercase outputs and does fine with mixed input casing so "Sentence sentence" is treated correctly by the program

// 227 bytes #include <stdio.h> int main(){int b,d,a['{']={};do{int c['{']={};while((b=getchar())!=10&&b!=EOF)c[b]++;for(d='A';d<='z';d++)if(c[d]>a[d])a[d]=c[d];}while(b!=EOF);for(b='A';b<='z';b++)for(d=a[b];d--;putchar(b));putchar(10);} 

Same as lowercase version but it always uppercase

// 228 bytes #include <stdio.h> int main(){int b,d,a['{']={};do{int c['{']={};while((b=getchar())!=10&&b!=EOF)c[b&~32]++;for(d='A';d<='Z';d++)if(c[d]>a[d])a[d]=c[d];}while(b!=EOF);for(b='A';b<='Z';b++)for(d=a[b];d--;putchar(b));putchar(10);} 

Explanation

The 'a' array is used to keep track minimal count of each letter required to able to make up any lines up to current line. The inner 'c' array (which reinitialized to 0 at start of line iteration) is used to keep track current counter.

Then the inner "getchar" loop is the loop reading input and increment the corresponding counter with the ASCII value as its index.

Then at the end of line iteration, it would compare each letter and does "max" operation (essentially a > b ? a : b) to update the count of minimal letters needed.

And the end it iterates from letter A to Z, and uses ASCII value to index to array. If its non zero then the printing loop essentially loops 'counter' times and does putchar that many times of the current character. The way it was iterated make it naturally sorted at output therefore no need for sorting.

Right before returning the main function, it puts a newline. Finishing the program.

Note: the 'b' and 'd' variable are temporary and used at multiple places for different purposes. It does not need initialization at definition time because it always initialized before used through unconditional assignments.

Uiua, 25 chars 20 chars 21 chars

ver3: +@a⊚↘55/↥⬚0⊜°⊚⊸±-@\n⌵

ver2: +@*↘2⊚/↥⬚0⊜°⊚⊸±-@\n⌵

ver1: +@a⊚/↥⬚0⊜(°⊚-@A▽⊸±⌵)⊸≠@\n

Kotlin, 189 bytes

lines().map{it.filter{it.isLetter()}.groupingBy{it}.eachCount()}.fold(mutableMapOf<Char,Int>()){r,i->i.map{(t,u)->r[t]=maxOf(r[t] ?:0,u)} r}.flatMap{(k,v)->(0..v-1).map{k}}.joinToString("") 

Beautified

lines() .map { it.filter { it.isLetter() }.groupingBy { it }.eachCount() } .fold(mutableMapOf<Char, Int>()) { r, i -> i.map { (t, u) -> r[t] = maxOf(r[t] ?: 0, u)} r } .flatMap { (k, v) -> (0..v-1).map { k } } .joinToString("") 

Test

fun String.f() = lines().map{it.filter{it.isLetter()}.groupingBy{it}.eachCount()}.fold(mutableMapOf<Char,Int>()){r,i->i.map{(t,u)->r[t]=maxOf(r[t] ?:0,u)} r}.flatMap{(k,v)->(0..v-1).map{k}}.joinToString("") fun main(args: Array<String>) { val i = """hello i love cat i love dog i love mommy mommy loves daddy""" println(i.f().map { it }.sorted().joinToString("")) println("acdddeghillmmmoostvyy") } 

TIO

TryItOnline

C# / LINQPad, 181 bytes

In C# Expression mode; assumes input file is named a (and probably in the LINQPad Program Files folder)

string.Join("",File.ReadAllLines("a").SelectMany(s=>s.ToUpper().Where(c=>c>64&&c<91).GroupBy(c=>c)).GroupBy(g=>g.Key).Select(g=>new string(g.Key,g.Max(x=>x.Count()))).OrderBy(s=>s)) 

Ungolfed

string.Join("", // concat all substrings, with no separator File.ReadAllLines("a") // read all lines from text file called 'a' .SelectMany( // apply function to each subset and union into a single set s => s.ToUpper() // convert strings to uppercase .Where(c => c > 64 && c < 91) // shorter than char.IsLetter(c) for all uppercase .GroupBy(c => c) // group on each character in the string ) .GroupBy(g => g.Key) // group again on each character (I'd love to get rid of this...) .Select(g => new string(g.Key, g.Max(x => x.Count()))) // string(char, count) constructor build repeating-char string .OrderBy(s => s) // sorted set required ) 

Input (text file called a)

Hello I love cat I love dog I love mommy Mommy loves daddy 

Output

ACDDDEGHILLMMMOOSTVYY 

C, 298 bytes

(242 bytes by not counting newlines)

Array D keeps tally of letters in each line, then the maximum count of each letter is copied into array C.

char c; int j,n; char C[26]; char D[26]; int main() { char a='a'; while((c=getchar())>=0) { c=tolower(c); if(c>=a&&c<='z'){j=c-a;D[j]++;} if(c=='\n'){ for(j=0;j<26;j++){ if(D[j]>C[j]) {C[j]=D[j];} D[j]=0; } } } for(j=0;j<26;j++) { n=C[j]; while(n--) { putchar(a+j); } } } 

Note: I just discovered Notepad++ which gives my character count, counts newlines as 2 chars. Should these be subtracted?

Stax, 8 bytes

ü2lLÜ▀⌂æ 

Run and debug it

1. Reduce the array of inputs using a multiset union operation.
2. Sort the resulting characters.
3. Remove spaces.

PHP, 116 bytes

foreach(file(T)as$y=>$s)for($i=0;~$c=ucfirst($s[$i++]);)$$c[$y]++;for($c=A;!$c[1];$c++)echo str_repeat($c,max($$c)); 

assumes filename T. Run with -nr.

breakdown

foreach(file(T)as$y=>$s) # loop through lines of file for($i=0;~$c=ucfirst($s[$i++]);) # loop through line characters $$c[$y]++;	# increment counter ($A..$Z)	for($c=A;!$c[1];$c++)	# loop $c through uppercase letters	echo str_repeat($c,max($$c)); # get max from $A, $B etc, use as multiplier for str_repeat 

JavaScript, 105 104 bytes

Takes input as an array of character arrays and returns a string.

a=>[...new Set(a+``)].sort().map(c=>c.repeat(a.map(r=w=>r=w.map(l=>o+=c>{}&c==l,o=0)|o<r?r:o)|r)).join`` 

Try it online

Pyth, 14 10 bytes

[email protected] 

Accepts input as lowercase strings. Try it online here.

[email protected] Implicit: .z=input as list of strings, G=lowercase alphabet m G Map each letter in G, as d, using: L .z In each string in .z ... @ d ... keep only those characters which match d S Sort by length e Take the last element (i.e. longest) s Concatenate into string, implicit print 

Edit: golfed 3 bytes. Previous version: sm*[email protected]

Vyxal s, 5 bytes

ɾƒÞ∪s 

Try it Online!