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.

解答

用树的递归解决

/**
* 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) {
if(root==null){
return 0;
}
return sum(root,0);
} public int sum(TreeNode node,int parentVal){
int sum=0;
int temp=parentVal*10+node.val;
if(node.left==null&&node.right==null){
sum=temp;
}
if(node.left!=null){
sum+=sum(node.left,temp);
}
if(node.right!=null){
sum+=sum(node.right,temp);
}
return sum;
}
}

---EOF---

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