【Leetcode】Sqrt(x)

Implement int sqrt(int x).

Compute and return the square root of x.

class Solution {
public:
    int sqrt(int x) {
        if (x < 2) return x;
        int start = 1, end = x / 2;
        int last_mid; // 记录最近一次mid, 无整数解时输出近似解，下取整
        while(start <= end) {
            int mid = (start + end) / 2;
            if(x / mid > mid) { // 不要用x > mid * mid，会溢出
                start = mid + 1;
                last_mid = mid;
            } else if(x / mid < mid) {
                end = mid - 1;
            } else {
                return mid;
            }
        }
        return last_mid;
    }
};

二分查找。Morgen Stanley的电面就问了这个.