找出重复数字


Given an array nums containing n + 1 integers where each integer is between 1 and n (inclusive),
prove that at least one duplicate number must exist. Assume that there is only one duplicate number, find the duplicate one.

思路：借用二分查找的思路，令mid=low+(high-low)/2，记录cnt为数组中值小于等于mid的个数，如果cnt>mid，重复的数字肯定在1...mid之间；否则，重复的数字在mid+1,...high之间

class Solution {
public:
int findDuplicate(vector<int>& nums) {
int len=nums.size();
if(len<=1)
return 0;
int low=1;
int high=len-1;
while(low<high)
{
int mid=low+(high-low)/2;
int cnt=0;
for(int i=0;i<len;i++)
{
if(nums[i]<=mid)
cnt++;

}
if(cnt<=mid)
low=mid+1;
else
high=mid;
}
return low;
}
};