【Leetcode】Sqrt(x)

int sqrt(int 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;
}
};