Java O(n) constant extra space solution

  • 0

    The basic idea behind this solution is, since numbers in array nums are picked between 0~n-1, so n must be equal to nums.length + 1. The sum from 0 to n-1 is (n-1)*n/2, we just need to calculate the sum for all numbers in nums (sum2) and then use sum to minus sum2 to get the missing element.

    public int missingNumber(int[] nums) {
            int n = nums.length + 1;
            int sum = (n-1)*n/2;
            int sum2 = 0;
            for(int i = 0; i < nums.length; i++){
                sum2 += nums[i];
            return sum - sum2;

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