a to the power of b

public class Solution {
  public long power(int a, int b) {
    // Write your solution here
    if (b == 0) return 1;
    long half = power(a, b/2);
    if (b % 2 == 0) {
        return half * half;
    } else {
        return half * half * a;
    }
  }
}

Q: Evaluate a to the power of b, assuming both a and b are integers and b is non-negative. 

 

User recursion to advance the process, reduce the time complexity to O(logb), instead of O(b).

Inside recursion:

　　Base case is when b == 0, return 1.

　　use b % 2 to determine if odd or even.

　　notice the type of return value. In this problem, is "long".