Leetcode 268. Missing Number

文章作者：Tyan
博客：noahsnail.com  |  CSDN  |  简书

1. Description

2. Solution

• Version 1

class Solution {
public:
    int missingNumber(vector<int>& nums) {
        int flag[nums.size() + 1] = {0};
        for(int i = 0; i < nums.size(); i++) {
            flag[nums[i]] = 1;
        }
        for(int i = 0; i <= nums.size(); i++) {
            if(flag[i] == 0) {
                return i;
            }
        }
    }
};

• Version 2

class Solution {
public:
    int missingNumber(vector<int>& nums) {
        int x = 0;
        for(int i = 0; i < nums.size(); i++) {
            x = x ^ i ^ nums[i];
        }
        x ^= nums.size();
        return x;
    }
};

• Version 3

class Solution {
public:
    int missingNumber(vector<int>& nums) {
        int n = nums.size();
        int result = n * (n + 1) / 2;
        for(int i = 0; i < nums.size(); i++) {
            result -= nums[i];
        }
        return result;
    }
};

Reference

1. https://leetcode.com/problems/missing-number/description/