LeetCode_sqrt(x)

class Solution {
public:
    int sqrt(int x) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
    if(x < 0 ) return -1;
    if(x == 0) return 0;
    if(x >= 1 && x <= 3) return 1;
    
    double start = 2.0;
    double next =  0.5 *(start + x/start);
    while(abs(start * start - x) > 0.000001){
        start = next;
        next = 0.5 *(start + x/start);
    }
    
    return int(start);
    }
};

两种方法的详细分析： http://www.cnblogs.com/AnnieKim/archive/2013/04/18/3028607.html