LeetCode Problem 169: Majority Element查找多数元素

描述：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.

思路1：Moore voting algorithm--每找出两个不同的element，就成对删除即count--，最终剩下的一定就是所求的。时间复杂度：O(n)

class Solution {
public:
int majorityElement(vector<int> &num) {

int elem = 0;
int count = 0;

for(int i = 0; i < num.size(); i++)  {

if(count == 0)  {
elem = num[i];
count = 1;
}
else    {
if(elem == num[i])
count++;
else
count--;
}

}
return elem;
}
　　};

思路2：随机挑选一个元素，检查是否是多数元素。时间复杂度：Average：O(n)。期望查找次数 <2

class Solution {
public:
int majorityElement(vector<int> &num) {

int count = 0;

for(;;) {
if(num.size() == 1)
return num[0];
else    {
int i = rand() % (num.size() - 1);
for(int j = 0; j < num.size(); j++) {
if(num[j] == num[i])
count++;
}
if(count > (num.size() / 2))
return num[i];
else    {
count = 0;
continue;
}
}
}
}
　　};

附LeetCode建议解决方案：