[Math]Pow(x, n)

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;
    }
};

Next challenges: (M) Sqrt(x)