《leetCode》：Sum Root to Leaf Numbers

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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

第一步：找出所有的从root到叶子节点的路径
第二步：求和

实现代码如下：

/*** Definition for a binary tree node.* public class TreeNode {*     int val;*     TreeNode left;*     TreeNode right;*     TreeNode(int x) { val = x; }* }*/
public class Solution {private List<List<Integer>> res=new ArrayList<List<Integer>>();//用来保存所有的路径public int sumNumbers(TreeNode root) {if(root==null){return 0;}//第一步：找出所有的路径sumNumbersHelper(root,new ArrayList<Integer>());//求和return sumAllList(res);}private int sumAllList(List<List<Integer>> listList) {if(listList==null){return 0;}int sum=0;int listSum=0;for(List<Integer> temp:listList){listSum=0;//注意：要在这里初始化为零for(Integer num:temp){listSum=listSum*10+num;}sum+=listSum;}return sum;}private void sumNumbersHelper(TreeNode root,List<Integer> list) {if(root==null){return;}list.add(root.val);if(root.left==null&&root.right==null){//到达叶子节点，保存此条路径           res.add(list);return ;}else{sumNumbersHelper(root.left,new ArrayList<Integer>(list));sumNumbersHelper(root.right,new ArrayList<Integer>(list));}}
}

小结

原以为这道题自己做不出来的，写了写着思路就开了，太开兴了，哈哈

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