[LeetCode][Java] Sum Root to Leaf Numbers

標籤：leetcode   java   sum root to leaf num   

題目：

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.

題意：

給定一棵二叉樹，僅僅包含0-9的數字元素，每一條從根節點到葉子節點的路徑都可以代表一個數.

舉個例子一條從根節點到葉子節點的路徑為1->2->3代表數為123.

找出所有的從根到葉子節點路徑中所表示的數的和。

比如給定：

    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.

演算法分析：

通過遞迴，思路比較清晰，主要就是考慮遞迴條件和結束條件。直接看代碼，比較好理解。

AC代碼：

<span style="font-family:Microsoft YaHei;font-size:12px;">/** * Definition for binary tree * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */ //又是遞迴public class Solution {    int sum = 0;    public int sumNumbers(TreeNode root)     {        if (root == null) return 0;        run(root, 0);        return sum;    }    public void run(TreeNode root, int num)     {        num = 10 * num + root.val;        if (root.left == null && root.right == null)             sum += num;        if (root.left != null)             run(root.left, num);        if (root.right != null)            run(root.right, num);    }}</span>

著作權聲明：本文為博主原創文章，轉載註明出處

[LeetCode][Java] Sum Root to Leaf Numbers