[LeetCode] Missing Number

最新推荐文章于 2021-11-06 23:49:58 发布

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最新推荐文章于 2021-11-06 23:49:58 发布

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原文链接：https://yq.aliyun.com/articles/331376

本文介绍了通过位操作、数组重排及数学技巧三种方法来找出数组中缺失的一个数字。位操作法通过异或运算实现；数组重排法通过循环交换元素到正确位置来查找缺失值；数学技巧法则利用等差数列求和公式减去现有数组总和得到缺失的数字。

There are three methods to solve this problem: bit manipulation, rearrangement of the array, and math tricks.

Bit Manipulation

1 class Solution {
2 public:
3     int missingNumber(vector<int>& nums) {
4         int ans = nums.size(), i = 0;
5         for (int num : nums)
6             ans ^= (num ^ (i++));
7         return ans;
8     }
9 };

Rearrangement

 1 class Solution {
 2 public:
 3     int missingNumber(vector<int>& nums) {
 4         int n = nums.size(), r = n;
 5         for (int i = 0; i < n; i++) {
 6             while (nums[i] != i) {
 7                 if (nums[i] == n) {
 8                     r = i;
 9                     break;
10                 }
11                 swap(nums[i], nums[nums[i]]);
12             }
13         }
14         return r;
15     }
16 };

Math

1 class Solution {
2 public:
3     int missingNumber(vector<int>& nums) {
4         int n = nums.size(), ans = n * (n + 1) / 2;
5         for (int num : nums) ans -= num;
6         return ans;
7     }
8 };