Implement pow(x, n).

answer:

class Solution {public:    double myPow(double x, int n) {     if(n==0) return 1;    if(n == INT_MIN){        if(x == 1 || x == -1) return 1;        else  return 0;    }    if(n<0) {        n = -n;        x = 1/x;    }    double ans = 1;    while(n>0){        if(n & 1) ans *= x;        x *= x;        n /= 2;    }    return ans;    }};