50. Pow(x, n)**

Implement pow(x, n).

1. nest myPow

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double myPow(double x, int n) {    if(n<0) return 1/x * myPow(1/x, -(n+1));    if(n==0) return 1;    if(n==2) return x*x;    if(n%2==0) return myPow( myPow(x, n/2), 2);    else return x*myPow( myPow(x, n/2), 2);}

2. double myPow

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double myPow(double x, int n) {     if(n==0) return 1;    double t = myPow(x,n/2);    if(n%2) return n<0 ? 1/x*t*t : x*t*t;    else return t*t;}

3. double x

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double myPow(double x, int n) {     if(n==0) return 1;    if(n<0){        n = -n;        x = 1/x;    }    return n%2==0 ? myPow(x*x, n/2) : x*myPow(x*x, n/2);}

4. iterative one

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double myPow(double x, int n) {     if(n==0) return 1;    if(n<0) {        n = -n;        x = 1/x;    }    double ans = 1;    while(n>0){        if(n&1) ans *= x;        x *= x;        n >>= 1;    }    return ans;}

5. bit operation