Main34.java

package JZOffer2;

import java.util.*;

public class Main34 {
    List<List<Integer>> res = new LinkedList<>();
    Deque<Integer> path = new LinkedList<>();
    public List<List<Integer>> pathSum(TreeNode root, int target) {
        dfs(root, target);
        return res;
    }

    void dfs(TreeNode root, int target){
        if(root == null){
            return;
        }
        path.offerLast(root.val);
        target -= root.val;
        if(root.left == null && root.right == null && target == 0){
            res.add(new LinkedList<>(path));
        }
        dfs(root.left, target);
        dfs(root.right, target);
        path.pollLast();
    }
}

class Main34_1{
    List<List<Integer>> ret = new LinkedList<List<Integer>>();
    Map<TreeNode, TreeNode> map = new HashMap<TreeNode, TreeNode>();

    public List<List<Integer>> pathSum(TreeNode root, int target) {
        if(root == null){
            return ret;
        }
        Queue<TreeNode> queueNode = new LinkedList<TreeNode>();
        Queue<Integer> queueSum = new LinkedList<Integer>();
        queueNode.offer(root);
        queueSum.offer(0);
        while (!queueNode.isEmpty()){
            TreeNode node = queueNode.poll();
            int rec = queueSum.poll() + node.val;
            if (node.left == null && node.right == null) {
                if (rec == target) {
                    getPath(node);
                }
            } else {
                if(node.left != null){
                    map.put(node.left, node);
                    queueNode.offer(node.left);
                    queueSum.offer(rec);
                }
                if(node.right != null){
                    map.put(node.right, node);
                    queueNode.offer(node.right);
                    queueSum.offer(rec);
                }
            }
        }
        return ret;
    }

    private void getPath(TreeNode node) {
        List<Integer> temp = new LinkedList<Integer>();
        while (node != null) {
            temp.add(node.val);
            node = map.get(node);
        }
        Collections.reverse(temp);
        ret.add(new LinkedList<Integer>(temp));
    }
}