376

2017.9.28

先用递归的办法找到所有的根节点到叶子节点的路径。

再一一计算和。

/** * Definition of TreeNode: * public class TreeNode { *     public int val; *     public TreeNode left, right; *     public TreeNode(int val) { *         this.val = val; *         this.left = this.right = null; *     } * } */public class Solution {    /*     * @param root: the root of binary tree     * @param target: An integer     * @return: all valid paths     */    public List<List<Integer>> pathToLeaf(TreeNode root){List<List<Integer>> res = new LinkedList<>();if(root == null){return res;}if(root.left == null && root.right == null){List<Integer> tmp = new LinkedList<Integer>();tmp.add(root.val);res.add(tmp);return res;}if(root.left != null){List<List<Integer>> resLeft = pathToLeaf(root.left);for(List<Integer> list: resLeft){List<Integer> tmp = new LinkedList<Integer>();tmp.add(root.val);tmp.addAll(list);res.add(tmp);}}if(root.right != null){List<List<Integer>> resRight = pathToLeaf(root.right);for(List<Integer> list: resRight){List<Integer> tmp = new LinkedList<Integer>();tmp.add(root.val);tmp.addAll(list);res.add(tmp);}}return res;}public List<List<Integer>> binaryTreePathSum(TreeNode root, int target) {        // write your code hereList<List<Integer>> res = new LinkedList<>();if(root == null){return res;}List<List<Integer>> path = pathToLeaf(root);for(List<Integer> list : path){    //System.out.println(list);int sum = 0;for(Integer num : list){sum = sum + num;}if(sum == target){res.add(list);}}return res;    }}