【LeetCode】Path Sum II

<span style="font-size:18px;">/**LeetCode Path Sum II
* 给定一棵二叉树，和一个目标值，找到值相加等于目标值的所有路径的集合
* 遍历所有路径，找到值符合的
* Definition for binary tree
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*
*/
package javaTrain;

import java.util.ArrayList;
import java.util.List;

public class Train11 {
public List<List<Integer>> pathSum(TreeNode root, int sum) {
List<List<Integer>> lists = new ArrayList();
List<Integer> list = new ArrayList();
help(root,sum,lists,list);
return lists;
}
private void help(TreeNode root,int sum,List<List<Integer>> lists,List<Integer> list){
if(root == null) return;
list.add(root.val);
if(root.left == null && root.right == null && root.val == sum){
List<Integer> newList = new ArrayList(list);
lists.add(newList);
//return 	不能在这里返回，因为list中有这层的叶节点，因为还要找别的路径，所以的回溯到上一节点
}
help(root.left,sum-root.val,lists,list);
help(root.right,sum-root.val,lists,list);
list.remove(list.size()-1);	//在这，将这层节点从list中去除
}
}
</span>