69. Sqrt(x)

Implement int sqrt(int x).

Compute and return the square root of x.

x is guaranteed to be a non-negative integer.

 

Example 1:

Input: 4
Output: 2

 

Example 2:

Input: 8
Output: 2
Explanation: The square root of 8 is 2.82842..., and since we want to return an integer, the decimal part will be truncated.


实现sqrt


C++:

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

 

C++（37ms）：

class Solution {
public:
    int mySqrt(int x) {
        long r = x ;
        while(r*r > x){
            r = (r + x/r) /2 ;
        }
        return r ;
    }
};