Sum Root to Leaf Numbers, Leetcode 解题笔记

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.

还是DFS,维护一个和num,每深入一层num*10+当前值,到叶子节点时将num加入sum中。

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