the first number is set by me and the other numbers by the method ,and every number is shown only one time
It looks like you are after a shuffling algorithm. The following category on NSMutableArray will do the job:
@interface NSMutableArray (Shuffling) - (void)shuffle; @end @implementation NSMutableArray (Shuffling) - (void)shuffle { // Fisher–Yates shuffle (modern algorithm) // To shuffle an array a of n elements (indexes 0..n-1): // for i from n − 1 downto 1 do // j <-- random integer with 0 <= j <= i // exchange a[j] and a[i] // http://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle for (int i = [self count] - 1; i >= 1; i--) { int j = arc4random() % (i + 1); [self exchangeObjectAtIndex:j withObjectAtIndex:i]; } } @end
Your requirement is that the number in the first position of the array is fixed (given by you). Then, you can do something like this:
Populate the array with all numbers between minValue and maxValue (both included) except for firstValue.
Shuffle the array.
Insert firstValue at the first position in the array.
Resulting in the following code:
NSInteger minValue = 5; NSInteger maxValue = 10; NSInteger firstValue = 9; // minValue <= firstValue <= maxValue // populate the array with all numbers between minValue // and maxValue (both included) except for firstValue NSMutableArray *ary = [NSMutableArray array]; for (int i = minValue; i < firstValue; i++) { [ary addObject:[NSNumber numberWithInt:i]]; } for (int i = firstValue + 1; i <= maxValue; i++) { [ary addObject:[NSNumber numberWithInt:i]]; } // --> (5,6,7,8,10) // shuffle the array using the category method above [ary shuffle]; // insert firstValue at the first position in the array [ary insertObject:[NSNumber numberWithInt:firstValue] atIndex:0]; // --> (9,x,x,x,x,x)
