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import java.io.*;
import java.util.*;

class Solution {
  public static void main(String[] args) {
    Solution solution = new Solution();
     int[][] input = {
          null,
          {},
          {1},
          {0,1},
          {0,0,0,1},
          {1,1,1,1,1,1},
          {0},
          {0,0,0,1,1}, 
          {0,1,1,1,1,}
        };
    for(int i=0;i<input.length;i++) {
       System.out.println("Input: " + Arrays.toString(input[i]) + 
                        ", Result: " +  solution.count1s(input[i]));
    }
  }
  
  public int count1s(int[] input) {
    if(input == null || input.length < 1){
      return 0;
    }

    return count1s(input, 0, input.length-1);
  }
  
  private int count1s(int[] input, int start, int end) {
    if(start > end) {
      return 0; 
    }
    
    if(input[end] == 0){
      return 0;
    }
    if(input[start] == 1) {
      return end - start +1;
    }
    int mid = (start + end)/2;
    return count1s(input,start,mid) + count1s(input,mid+1,end);
  }
}