113. Path Sum II.java

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public List<List<Integer>> pathSum(TreeNode root, int sum) {
        List<List<Integer>> result = new LinkedList<List<Integer>>();
        List<Integer> currentResult = new LinkedList<Integer>();
        findPathSum(root, sum, currentResult, result);
        return result;
    }
    
    private void findPathSum(TreeNode root, int sum, List<Integer> currentResult, List<List<Integer>> result){
        if(root == null) return;
        
        currentResult.add(root.val);
        if(root.left == null && root.right == null && sum == root.val){
            result.add(new LinkedList(currentResult));
        }else{
            findPathSum(root.left, sum - root.val, currentResult, result);
            findPathSum(root.right, sum - root.val, currentResult, result);
        }
        currentResult.remove(currentResult.size() - 1);
    }
}