Pow(x, n)

最新推荐文章于 2024-12-24 09:53:51 发布

转载最新推荐文章于 2024-12-24 09:53:51 发布 · 65 阅读

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原文链接：http://www.cnblogs.com/zengzy/p/5043784.html

Total Accepted: 73922 Total Submissions: 269855 Difficulty: Medium

Implement pow(x, n).

(M) Sqrt(x)

1.递归

/*
n = 0, <0 , >0
x = 0 ,x>0,x<0
*/
class Solution {
public:
    double myPowWithPositiveExp(double x,unsigned int n)
    {
        if(n==1){
            return x;
        }
        double res = myPowWithPositiveExp(x,n>>1) ;
        res = res * res;
        return 1&n ? res * x : res;
    }
    double myPow(double x, int n) {
        if(n==0){
            return 1;
        }
        if(n<0){
            return 1/ myPowWithPositiveExp(x,-n)   ;
        }
        return myPowWithPositiveExp(x,n)   ;  
    }
};

2.迭代

/*
n = 0, <0 , >0
x = 0 ,x>0,x<0
*/
class Solution {
public:
    double myPow(double x, int n) {
        if(n==0){
            return 1;
        }
        long long int m = fabs(n);
        double res = 1;
        bool first = true;
        while(m){
            first ?  x *= 1,first=false : x *= x;
            if(1&m){
                res *= x;
            }
            m = m>>1;
        }
        return  n<0 ?  1/res : res;  
    }
};