69. Sqrt(x)

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.

难度：easy

题目：
实现sqrt.
计算并返回x的开方，x保证非负整。
由于返回的类型是整数，十进制数只返回整数部分。

Runtime: 22 ms, faster than 30.19% of Java online submissions for Sqrt(x).
Memory Usage: 27 MB, less than 99.23% of Java online submissions for Sqrt(x).

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