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.
方法一：
采用二分法

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

方法二：采用牛顿迭代法

C++
int mySqrt(int x) {
        //牛顿迭代法
        if(x <= 1)return x;
        long res = x;
        while(res*res > x)
        {
            res = (res + x/res)/2;
        }
        return res;
    }