Sqrt(x)

Implement int sqrt(int x).

Compute and return the square root of x.

二分法，但是用除法来检测，避免溢出。

public class Solution {
    //Time: O(logn)  Space: O(1)
    public int sqrt(int x) {
        if (x == 0 || x == 1) {
            return x;
        }
        
        int left = 1;
        int right = x;
        while (left + 1 < right) {
            int mid = left + (right - left) / 2;
            if (x / mid == mid) {
                return mid;
            } else if (x / mid > mid) {
                left = mid;
            } else {
                right = mid;
            }
        }
        if (x / right > right) {
            return right;
        } else {
            return left;
        }
    }
}