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

.

求根到子树的路径的所有和。

常用回溯法。

每当dfs访问到子树时，把和加上即可。

int sum=0;
public int sumNumbers(TreeNode root)
{
if(root==null)
return 0;

inorder(root, String.valueOf(root.val));
return sum;
}

private void inorder(TreeNode t,String s)
{
if(t.left!=null)
inorder(t.left, s+t.left.val);

if(t.left==null&&t.right==null)
sum+=Integer.parseInt(s);

if(t.right!=null)
inorder(t.right, s+t.right.val);

}