leetcode: sqrt

Implement int sqrt(int x).

Compute and return the square root of x.

这道题目就是个二分查找题目，一定要记住

class Solution {
public:
    int sqrt(int x) {
        
        if (x < 1)
            return 0;
            
        if (x == 1 || x == 2 || x == 3)
            return 1;

        long long begin = 0;
        long long end   = x;

        long long mid = 1;
        while (true)
        {
            mid = (begin+end)/2; 

            if ((mid*mid == x) || (mid*mid < x && (mid+1)*(mid+1) > x))
                return mid;

            if (mid*mid < x)
            {
                begin = mid;
            }
            else
            {
                end = mid;
            }
        }
    }
};