leetcode 69 implement the sqrt(x)

Problem: Implement int sqrt(int x).

Compute and return the square root of x.

Solution: 二分法思想，要特别注意细节部分，有可能的溢出。

class Solution {public:    int mySqrt(int x) {                if(x < 0)            return -1;        if(x == 0)            return 0;        if(x == 1)            return 1;               long long  left = 0;       long long  right = x /2 ;                while(left <= right){           long long int mid = left + (right - left)/2;            long long int val = mid*mid;            if(val == x) return mid;            else if(val < x)             {left = mid + 1;}            else {right = mid -1;}                    }                long long  tmp = left*left;        if(tmp <= x)            return left;        else            return right;            }};