leetcode69---Sqrt(x)（求x的平方根）

问题描述：

Implement int sqrt(int x).

Compute and return the square root of x.

问题求解：

二分法。O（logN）

class Solution {
public:
    int mySqrt(int x) {
        long long  low =1;
        long long  high=x;
        long long  tmp;//用于和x比较
        while(low < high)
        {//二分法查找1~x里边的数，平方为tmp,与x比较
            long long mid = low + (high-low)/2;
            tmp = mid*mid;
            if(tmp==x) return mid;
            else if(tmp > x) high=mid-1;
            else low=mid+1;
        }
        tmp = high*high;
        if(tmp > x) return high-1;
        else return high;
    }
};