剑指offer其他算法39.数组中出现次数超过一半的数字

Posted 2021-02-28 trevo

题目链接：https://leetcode-cn.com/problems/shu-zu-zhong-chu-xian-ci-shu-chao-guo-yi-ban-de-shu-zi-lcof/

循环抵消

统计数字出现的个数cnt = 0, val = -1;
遍历数组中每个数字x
    如果val = x, cnt++
    如果val != x, 
        1. cnt != 0, cnt--; 
        2. cnt == 0, 更新val和cnt
时间复杂度O(N) 空间复杂度O(1)

class Solution {
public:
    int majorityElement(vector<int>& nums) {
        int cnt = 0, val = -1;
        for (auto x : nums)
        {
            if (x == val)   cnt ++ ;
            else
            {
                if (cnt)    cnt -- ;
                else
                {
                    cnt = 1;
                    val = x;
                }
            }
        }
        return val;
    }
};