【LeetCode】169 - Majority Element

Given an array of size n, find the majority element. The majority element is the element that appears more than ⌊ n/2 ⌋ times.

You may assume that the array is non-empty and the majority element always exist in the array.

Solution 1: 使用map计数

 class Solution {
 public:
     int majorityElement(vector<int>& nums) {　　　　//runtime:32ms
         map<int, int> nums_count;
         vector<int>::iterator iter=nums.begin();

         while(iter!=nums.end()){
             ++nums_count[*iter];
             iter++;
         }

         int n=nums.size();

         map<int, int>::iterator ite=nums_count.begin();
         //int max=ite->second;
         while(ite!=nums_count.end()){
             if(ite->second>n/){
                 return ite->first;
             }
             ite++;
         }
     }
 };

Solution 2: 每找出两个不同的element就成对删除，最后可能剩两个元素或一个元素，必定都是所求

 class Solution {
 public:
     int majorityElement(vector<int>& nums) {    //runtime: 20ms
         int count=;
         int ret;
         for(int i=;i<nums.size();i++){
             if(count==){
                 ret=nums[i];
                 count++;
             }else{
                 if(nums[i]==ret)
                     count++;
                 else
                     count--;
             }
         }
         return ret;
     }
 };

扩展到⌊ n/k ⌋的情况，每k个不同的element进行成对删除