leetcode--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:
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]
]


dfs method:

public class Solution {
    public List<List<Integer>> pathSum(TreeNode root, int sum) {
        List<List<Integer> > paths = new ArrayList<List<Integer>>();
        List<Integer> oneSolution = new ArrayList<Integer>();
        if(root != null)
            dfs(root, 0, sum, oneSolution, paths);
        return paths;
    }
        
    private void dfs(TreeNode node, int accu, int sum, List<Integer> oneSolution, 
                     List<List<Integer>> paths) {
        accu += node.val;
        oneSolution.add(node.val);
        if(node.left == null && node.right == null && accu == sum) {
            List<Integer> copy = new ArrayList<Integer>();
            copy.addAll(oneSolution);
            paths.add(copy);
        }
        else{
            if(node.left != null) 
                dfs(node.left, accu, sum, oneSolution, paths);
            if(node.right != null)
                dfs(node.right, accu, sum, oneSolution, paths);
        }
        accu -= node.val;
        oneSolution.remove(oneSolution.size() - 1);    
    }
}

　　

bfs method:

public class Solution {
    public List<List<Integer>> pathSum(TreeNode root, int sum) {
        List<List<Integer> > result = new ArrayList<List<Integer> >();
		Map<TreeNode, List<Integer> > fromTreeNodeToList = new HashMap<TreeNode, List<Integer> >();
		Map<TreeNode, Integer> fromTreeNodeToSum = new HashMap<TreeNode, Integer>();
		if(root != null){
			Deque<TreeNode> nodes = new LinkedList<TreeNode>();
			nodes.add(root);
			List<Integer> startList = new ArrayList<Integer>();
			startList.add(root.val);
			fromTreeNodeToList.put(root, startList);
			fromTreeNodeToSum.put(root, root.val);
			while(nodes.peek() != null){
				TreeNode aNode = nodes.poll();
				if(aNode.left == null && aNode.right == null){
					if(fromTreeNodeToSum.get(aNode) == sum)
						result.add(fromTreeNodeToList.get(aNode));
				}
				else{
					int sumAtNode = fromTreeNodeToSum.get(aNode);
					List<Integer> listAtNode = fromTreeNodeToList.get(aNode);
					if(aNode.left != null){
						 List<Integer> newList = new ArrayList<Integer>();
						 newList.addAll(listAtNode);
						 newList.add(aNode.left.val);
						 fromTreeNodeToSum.put(aNode.left, sumAtNode + aNode.left.val);
						 fromTreeNodeToList.put(aNode.left, newList);
						 nodes.add(aNode.left);
					}
					if(aNode.right != null){
						 List<Integer> newList = new ArrayList<Integer>();
						 newList.addAll(listAtNode);
						 newList.add(aNode.right.val);
						 fromTreeNodeToSum.put(aNode.right, sumAtNode + aNode.right.val);
						 fromTreeNodeToList.put(aNode.right, newList);
						 nodes.add(aNode.right);
					}
				}
			}
		}
		return result;    
    }
}