lc50-Pow(x, n)

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注意负号的corner case，以及INT_MIN

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class Solution {
public:
    double myPow(double x, int n) {
        // if (n<0)    return 1/x*myPow(1/x, -(n+1));
        if (n==1)   return x;
        if (!n) return 1;
        double m = myPow(x, n/2);
        double t = (n<0)?1/x:x;
        if (n%2) return m*m*t;
        else return m*m;
    }
};
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class Solution {
public:
    double myPow(double x, int n) {
        if (n<0)    return 1/x*myPow(1/x, -(n+1));
        if (n==1)   return x;
        if (!n) return 1;
        double m = myPow(x, n/2);
        if (n%2) return m*m*x;
        else return m*m;
    }
};