牛客習題總結16

import java.util.*;
public class UnusualAdd {
public int addAB(int A, int B) {
             if(B==0)  {
             return A;
        }

        int sum = A ^ B; //相加但不進位
        int jin = (A & B) << 1; //進位但不相加
        return addAB(sum, jin);
  }
}