LeetCode Solutions : Path Sum I & II

Path Sum

Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.


For example:
Given the below binary tree and sum = 22,
              5
             / \
            4   8
           /   / \
          11  13  4
         /  \      \
        7    2      1
return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.

/** * Definition for binary tree * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    public boolean hasPathSum(TreeNode root, int sum) {        if(root==null)return false;if(root.left==null&&root.right==null)return sum==root.val?true:false;return hasPathSum(root.left,sum-root.val)||hasPathSum(root.right,sum-root.val);    }}

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]
]

/** * 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>> results=new ArrayList<ArrayList<Integer>>();if(root==null)return results;helper(results,new ArrayList<Integer>(),root,sum);return results;    }    private void helper(ArrayList<ArrayList<Integer>> results,ArrayList<Integer> path,TreeNode root,int sum){if(root==null)return;path.add(root.val);if(root.left==null&&root.right==null){if(root.val==sum){ArrayList<Integer> temp=new ArrayList<Integer>(path);results.add(temp);}}helper(results,path,root.left,sum-root.val);helper(results,path,root.right,sum-root.val);path.remove(path.size()-1);}}