113.路径总和II

方法一：深度优先搜素

/**
 * Definition for a binary tree node.
 * 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;
 *     }
 * }
 */
class Solution {
    List<List<Integer>> ans = new LinkedList<List<Integer>>();
    Deque<Integer> path = new LinkedList<Integer>();
    public List<List<Integer>> pathSum(TreeNode root, int targetSum) {
        dfs(root,targetSum);
        return ans;
    }
    public void dfs(TreeNode root,int targetSum){
        if(root == null){
            return;
        }
        path.offerLast(root.val);
        targetSum -= root.val;
        if(root.left == null && root.right == null && targetSum == 0){
            ans.add(new LinkedList<Integer>(path));
        }
        dfs(root.left,targetSum);
        dfs(root.right,targetSum);
        path.pollLast();
    }
}