69. Sqrt(x) （MATH）

A little trick is using i <= x / i for comparison, instead of i * i <= x, to avoid exceeding integer upper limit.

 

二分法查找比较快

 

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