Sum Root to Leaf Numbers ——Leetcode系列（十七）

最新推荐文章于 2020-08-21 10:38:58 发布

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本文介绍了一道经典的二叉树遍历问题——求所有从根节点到叶子节点的路径数值之和。通过递归算法，实现了对二叉树中每条路径数值的计算，并返回这些路径数值的总和。

Sum Root to Leaf Numbers

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.

Solution

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
    public class Solution {
        public int sumNumbers(TreeNode root){
        int sum = 0;
        if(root != null){
            List<String> list = subTreeNumbers(root);
            for(int i = 0; i < list.size(); i++){
                sum += Integer.valueOf(list.get(i));
            }
        }
        return sum;
    }

    private List<String> subTreeNumbers(TreeNode node){
        List<String> list = new ArrayList<String>();
        if(node.left != null){
            List<String> leftList = subTreeNumbers(node.left);
            for(int i = 0; i < leftList.size(); i++){
                list.add(node.val + leftList.get(i));
            }
        }
        if(node.right != null){
            List<String> rightList = subTreeNumbers(node.right);
            for(int i = 0; i < rightList.size(); i++){
                list.add(node.val + rightList.get(i));
            }
        }
        if(node.left == null && node.right == null){
            list.add("" + node.val);
        }
        return list;
    }

}

题目来源：https://oj.leetcode.com/problems/sum-root-to-leaf-numbers/