113. Path Sum II

Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.

For example:vGiven the below binary tree andsum = 22

              5
             / \
            4   8
           /   / \
          11  13  4
         /  \    / \
        7    2  5   1

return

[
   [5,4,11,2],
   [5,8,4,5]
]

思路：DFS递归，非常经典

public class Solution {
    public List<List<Integer>> pathSum(TreeNode root, int sum) {
        List<List<Integer>> res = new ArrayList<List<Integer>>();
        List<Integer> temp = new ArrayList<Integer>();
        DFS(root, res, temp, sum, 0);
        return res;
    }

    public void DFS(TreeNode root, List<List<Integer>> res, List<Integer> temp, int sum, int currSum){
        if (root == null){
            return;
        }

        temp.add(root.val);
        if (root.left==null && root.right==null && currSum+root.val==sum){
            res.add(new ArrayList<Integer>(temp));
        }else{
            DFS(root.left, res, temp, sum, currSum+root.val);
            DFS(root.right, res, temp, sum, currSum+root.val);
        }
        temp.remove(temp.size() - 1);
    }
}