PathSum.java

package dfs_bfs;

import java.util.Deque;
import java.util.LinkedList;
import java.util.List;

public class PathSum {
    List<List<Integer>> res = new LinkedList<>();
    Deque<Integer> path = new LinkedList<>();

    public List<List<Integer>> pathSum(TreeNode root, int targetSum) {
        // 深度优先遍历 targetSum -= root.val --> targetSum == 0 返回路径
        dfs(root, targetSum);
        return res;
    }

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

}

public class TreeNode {

    int val;
    TreeNode left;
    TreeNode right;

    TreeNode() {
    }

    TreeNode(int val) {
        this.val = val;
    }

    TreeNode(int val, TreeNode left, TreeNode right) {
        this.val = val;
        this.left = left;
        this.right = right;
    }
}