【leetcode】287. Find the Duplicate Number

題目：
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.

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思路：
二分法。抄的作業，看的博文https://www.cnblogs.com/grandyang/p/4843654.html。

全面剖析二分搜索算法：https://blog.csdn.net/zxc120389574/article/details/105714573

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代碼實現：

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

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參考：
https://www.cnblogs.com/grandyang/p/4843654.html