【leetcode】Sqrt(x)

class Solution {
public:
    int sqrt(int x) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        int sta=0,end=x;
        while(sta<=end)//等号不能丢
        {
            long long mid=(sta+end)/2;//也必须为long long
            long long square=mid*mid;//可能溢出，为long long
            if(square<x)
                sta=mid+1;
            else if(square>x)
                end=mid-1;
            else return mid;    
        }
        return end;
    }
};