Path Sum II.java

Path Sum IIOct 14 '12
Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.

For example:
Given the below binary tree and sum = 22,
              5
             / \
            4   8
           /   / \
          11  13  4
         /  \    / \
        7    2  5   1
return
[
   [5,4,11,2],
   [5,8,4,5]
]

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ArrayList<ArrayList<Integer>> pathSum(TreeNode root, int sum) {
    	ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
	if (root != null) {
	    ArrayList<Integer> path = new ArrayList<Integer>();
	    findPathSum(root, sum, result, path);
	}
	return result;
    }

    public void findPathSum(TreeNode root, int sum,
	ArrayList<ArrayList<Integer>> result, ArrayList<Integer> path) {
	if (root == null) return;
	if (root.left == null && root.right == null && root.val == sum) {
	    ArrayList<Integer> clone = new ArrayList<Integer>(path);
	    clone.add(root.val);
	    result.add(clone);
	} else {
	    path.add(root.val);
	    if (root.left != null) {
		findPathSum(root.left, sum - root.val, result, path);
	    }
	    if (root.right != null) {
		findPathSum(root.right, sum - root.val, result, path);
	    }
            path.remove(path.size() - 1);
	}
    }
}