Problem Path Sum II

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

Solution: 递归。

public List<List<Integer>> pathSum(TreeNode root, int sum) {
        List<List<Integer>> list = new ArrayList<List<Integer>>();
        if (root == null) return list;
        List<Integer> tmp = new ArrayList<Integer>();
        path(root, sum, list, tmp);
        return list;
    }
    public void path(TreeNode root, int sum, List<List<Integer>> list, List<Integer> tmp) {
        if (root == null) return;
        tmp.add(root.val);
        int leftsum = sum - root.val;

        if (leftsum == 0 && root.left == null && root.right == null) {
            list.add(new ArrayList<Integer>(tmp));
        }
        path(root.left, leftsum, list, tmp);
        path(root.right, leftsum, list, tmp);

        tmp.remove(tmp.size() - 1);
    }