leetcode - majority elements

leetcode - majority elements

给定size 为n的数组，查找出主元素，就是出现次数大于n/2次的元素。

1.

 int majorityElement(vector<int> &num) { 
std::map<int, int> im; 
for (int i = 0; i < num.size(); ++i){ 
map<int, int>::iterator it = im.find(num[i]);
 if (it == im.end()) 
{ im[num[i]] = 1; } 
else 
{ im[num[i]]++; } 
if (im[num[i]] > num.size()/2) 
{ return num[i]; } }
 return 0;}

2.

class Solution {
public:
int majorityElement(vector<int>& nums) {
int ret = nums[0];
int count = 1;
for(int i = 1; i < nums.size(); i ++)
{
if(nums[i] == ret)
count ++;
else
{
count --;
if(count == 0)
{
ret = nums[i];
count = 1;
}
}
}
return ret;
}
};

3. Moore's voting algorithm

int majorityElement(vector<int> &num) {    

int majorityIndex = 0;    

for (int count = 1, i = 1; i < num.size(); i++) 

{        

num[majorityIndex] == num[i] ? count++ : count--;        

if (count == 0) {           

majorityIndex = i;            

count = 1;      

}    

}    

return num[majorityIndex];

}

4.

class Solution {
2 public:
3     int majorityElement(vector<int> &num) {
4
5         int count = 0;
6
7         for(;;) {
8             if(num.size() == 1)
9                 return num[0];
10             else    {
11                 int i = rand() % (num.size() - 1);
12                 for(int j = 0; j < num.size(); j++) {
13                     if(num[j] == num[i])
14                         count++;
15                 }
16                 if(count > (num.size() / 2))
17                     return num[i];
18                 else    {
19                     count = 0;
20                     continue;
21                 }
22             }
23         }
24     }

5. int my_cmp(int a,int b)  {      return a > b;  }    int Solution::majorityElement(vector<int> &num)  {      sort(num.begin(),num.end(),my_cmp);      return num[num.size()/2];  }