Posts Tagged 【tree && dfs】Sum Root to Leaf Numbers

Sum Root to Leaf Numbers

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Question
Solution

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

.

/*
从根节点遍历，若遍历到叶子结点，则sum+其路径的所有权值和
当然，也可以把所有的遍历存储过来
参考http://blog.csdn.net/csu54zzg/article/details/45039961
*/
/**
* 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) {
return dfs(root,0);
}
private int dfs(TreeNode root, int sum) {
//注意(1,#,2)
if(root == null) return 0;
sum = sum*10+root.val;
if(root.left == null && root.right == null)
return sum;
return dfs(root.left,sum)+dfs(root.right,sum);
}
}

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