129. 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

.

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dfs

/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
public class Solution {
// private static int ret = 0;
private int dfs(TreeNode root,int ret){
if(root.left==null&&root.right==null)ret=ret+root.val;
if(root.left!=null){
root.left.val=10*root.val+root.left.val;
ret = dfs(root.left,ret);
}
if(root.right!=null){
root.right.val=10*root.val+root.right.val;
ret = dfs(root.right,ret);
}
return ret;
}
public int sumNumbers(TreeNode root) {
int ret = 0;
if(root==null)return ret;
return dfs(root,ret);

}
}