268. Missing Number

class Solution {public:    int missingNumber(vector<int>& nums) {        int nums_len = nums.size() - 1;        for(int i = 0; i <= nums_len; i++) {            if(abs(nums[i]) <= nums_len && nums[i] != INT_MIN) {                if(!nums[abs(nums[i])])  nums[abs(nums[i])] = INT_MIN;                else  nums[abs(nums[i])] = -1*nums[abs(nums[i])];            }                    else if(nums[i] == INT_MIN)                nums[0] = -1*nums[0];        }        for(int j = 0; j <= nums_len; j++)            if(nums[j] >= 0)                return j;        return nums_len + 1;    }};