_129.java

package com.fishercoder.solutions;

import com.fishercoder.common.classes.TreeNode;

import java.util.ArrayList;
import java.util.List;

/**Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number.

 An example is the root-to-leaf path 1->2->3 which represents the number 123.

 Find the total sum of all root-to-leaf numbers.

 For example,

 1
 / \
 2   3
 The root-to-leaf path 1->2 represents the number 12.
 The root-to-leaf path 1->3 represents the number 13.

 Return the sum = 12 + 13 = 25.

 */
public class _129 {
    public int sumNumbers(TreeNode root) {
        if(root == null) return 0;
        List<Integer> allNumbers = new ArrayList();
        dfs(root, new StringBuilder(), allNumbers);
        int sum = 0;
        for(int i : allNumbers){
            sum += i;
        }
        return sum;
    }

    private void dfs(TreeNode root, StringBuilder sb, List<Integer> allNumbers) {
        sb.append(root.val);
        if(root.left != null){
            dfs(root.left, sb, allNumbers);
        }
        if(root.right != null){
            dfs(root.right, sb, allNumbers);
        }
        if(root.left == null && root.right == null){
            allNumbers.add(Integer.parseInt(sb.toString()));
        }
        sb.deleteCharAt(sb.length()-1);
    }
    
    class more_concise_version {
        public int sumNumbers(TreeNode root) {
            return dfs(root, 0);
        }

        private int dfs(TreeNode root, int sum) {
            if (root == null) return 0;
            if (root.left == null && root.right == null) return sum * 10 + root.val;
            return dfs(root.left, sum * 10 + root.val) + dfs(root.right, sum * 10 + root.val);
        }
    }

}