leetcode：Path Sum II

/**
* Definition for binary tree
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/
public class Solution {

static int ans = 0;
static ArrayList<Integer> stack = new ArrayList<Integer>();
static ArrayList<ArrayList<Integer>> list = new ArrayList<ArrayList<Integer>>();

public ArrayList<ArrayList<Integer>> pathSum(TreeNode root, int sum) {
ans = 0;
stack.clear();
list.clear();
traverl(root, sum);
return list;
}

public static boolean isLeaf(TreeNode root){
return root.left == null && root.right == null;
}
static void traverl(TreeNode root, int sum){
if(root != null){
stack.add(root.val);
ans += root.val;
if(isLeaf(root) && ans == sum){
ArrayList<Integer> t = new ArrayList<Integer>();
for(int i = 0; i < stack.size();++i){
t.add(stack.get(i));
}
list.add(t);
}
traverl(root.left, sum);
traverl(root.right, sum);
stack.remove(stack.size() - 1);
ans -= root.val;
}
}
}