Fast power (template)

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Fast power （ Templates ）

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Time complexity O(logn);
Spatial complexity O(1);

double myPow(double x, int n) {
    
        if(n==0) return 1;
        double sum=1;
        long long m=abs(n);//long long  Type prevents n=-2^31 Take the timing and burst it int;
        while(m) {
    
            if(m&1) {
    
                if(n>0) sum*=x;
                else sum/=x;
            }
            m>>=1;
            x*=x;
        }
        return sum;
    }