【LeetCode】Sum Root to Leaf Numbers 解题报告

【题目】

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

.
【思路】

二叉树的穷尽搜索，递归法即可。

【Java代码】

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
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);
        }
    }
}