leetcode_78 Sqrt(x)

题目：

Implement int sqrt(int x).

Compute and return the square root of x, where x is guaranteed to be a non-negative integer.

Since the return type is an integer, the decimal digits are truncated and only the integer part of the result is returned.

Example 1:

Input: 4
Output: 2

Example 2:

Input: 8
Output: 2
Explanation: The square root of 8 is 2.82842..., and since 
             the decimal part is truncated, 2 is returned.

本文采用binary search

代码如下：

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