Why (n>>1) is error?

  • 0
    class Solution {
        double power(double x, int n) {
            if (n==0) return 1;
            double y = power(x, n>>1);
            if (n%2==0) return y*y;
            else return y*y*x;
        double pow(double x, int n) {
            if (n<0) return 1.0/power(x,-n);
            else return power(x,n);

    when input: x=1.0, n=-2147483648
    It can't AC, but if using(n/2) raplace (n>>1), it will get AC, why?

  • 0

    The reason can be explained as follows. power(x, -2147483648 ) will call power(x, -1073741824) which will call power(x, -536870912) which subsequently will call power(x,-1).
    Now -1>>1 will be equal to -1 but -1/2 will be equal to 0. Hence when using n>>1 your recursion will never terminate. It will give you stack overflow error. But in second case you recursion will terminate due to statement if (n==0) return 1; resulting in right answer.

    If you want to know why -1>>1=-1 try to find out bit representation of signed integer and how shift operator work on signed integer.

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