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【LeetCode】Single Number (2 solutions)
Single Number
Given an 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?
解法一:用map记录每个元素的次数,返回次数为1的元素
class Solution { public: map<int,int> m; int singleNumber(int A[], int n) { for(int i = 0; i < n; i ++) { map<int,int>::iterator it = m.find(A[i]); if(it == m.end()) m.insert(map<int,int>::value_type(A[i], 1)); else it->second = 2; } for(map<int,int>::iterator it = m.begin(); it != m.end(); it ++) { if(it->second == 1) return it->first; } } };
解法二:利用异或操作的结合律。同一数字异或自己结果为0.x^x=0
class Solution { public: int singleNumber(int A[], int n) { int sum = 0; for(int i = 0; i < n; i ++) sum ^= A[i]; return sum; } };
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