136. Single Number

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本文介绍了一种在非空整数数组中查找唯一出现一次元素的算法，该算法具备线性时间复杂度，且不使用额外内存。通过两个示例详细展示了如何在给定数组中找到唯一元素。

136. Single Number

Easy

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Given a non-empty array of integers, every element appears twice except for one. Find that single one.

Note:

Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?

Example 1:

Input: [2,2,1]
Output: 1

Example 2:

Input: [4,1,2,1,2]
Output: 4

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class Solution {
public:
    int singleNumber(vector<int>& nums) {
        int res=0;
        unordered_map<int,int> hash;
        for(int val:nums){
            hash[val]++;;
        }
        for(int val:nums){
            if(hash[val]==1) res=val;
        }
        return res;
    }
};

class Solution {
public:
    int singleNumber(vector<int>& nums) {
        int res=nums[0];
        for(int val=1;val<nums.size();val++){
           res=res^nums[val];
        }
        return res;
    }
};