Method dfs

NumberOfGoodLeafNodes.java:33–55

(TreeNode root, int distance)

class Solution {
    int res=0;
  public int[] dfs(TreeNode root, int distance){
        int leafDist[] = new int[11];
        if(root==null){
            return leafDist;
        }else if(root.left==null && root.right==null){
            leafDist[1] = 1;
            return leafDist;
        }
        int leftLeafDist[] = dfs(root.left,distance);
        int rightLeafDist[] = dfs(root.right,distance);

        for(int d1=1;d1<=distance;d1++){
            for(int d2=1;d2<=distance;d2++){
                if(d1+d2<=distance){ 
                    res += leftLeafDist[d1] * rightLeafDist[d2];
                }
            }    
        }
        for(int d=1;d<11;d++){
            leafDist[d] = leftLeafDist[d-1] + rightLeafDist[d-1];
        }
        return leafDist;
  }
  public int countPairs(TreeNode root, int distance) {
        dfs(root,distance);
        return res;