ProductOfArray.md

238. Product of Array Except Self

Given an array of n integers where n > 1, nums, return an array output such that output[i] is equal to the product of all the elements of nums except nums[i].

Solve it without division and in O(n).

For example, given [1,2,3,4], return [24,12,8,6].

Follow up: Could you solve it with constant space complexity? (Note: The output array does not count as extra space for the purpose of space complexity analysis.)

Java

public int[] productExceptSelf(int[] nums) {
    int[] result = new int[nums.length];
    int multiplier = 1;
    for (int i = 0; i < nums.length; i++) {
        result[i] = multiplier;
        multiplier *= result[i];
    }
    multiplier = 1;
    for (int i = nums.length - 1; i >= 0; i--) {
        result[i] *= multiplier;
        multiplier *= result[i];
    }
    return result;
}

Objective-C

- (NSArray *)prodcutExceptSelf:(NSArray *)nums {
    NSMutableArray *result = [[NSMutableArray alloc] init];
    int multiplier = 1;
    for (int i = 0; i < nums.count; i++) {
        result[i] = [NSNumber numberWithInt:multiplier];
        multiplier *= [nums[i] intValue];
    }
    multiplier = 1;
    for (int i = (int)nums.count - 1; i >= 0; i--) {
        int temp = [result[i] intValue] * multiplier;
        result[i] = [NSNumber numberWithInt: temp];
        multiplier *= [nums[i] intValue];
    }
    return result;
}