LeetCode – Sum Root to Leaf Numbers (Java)

Category: Algorithms >> Interview May 20, 2014

Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number. Find the total sum of all root-to-leaf numbers.

For example,

    1
   / \
  2   3

The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.
Return the sum = 12 + 13 = 25.

Java Solution - Recursive

This problem can be solved by a typical DFS approach.

public int sumNumbers(TreeNode root) {
    int result = 0;
    if(root==null)
        return result;
 
    ArrayList<ArrayList<TreeNode>> all = new ArrayList<ArrayList<TreeNode>>();
    ArrayList<TreeNode> l = new ArrayList<TreeNode>();
    l.add(root);
    dfs(root, l, all);
 
    for(ArrayList<TreeNode> a: all){
        StringBuilder sb = new StringBuilder();
        for(TreeNode n: a){
            sb.append(String.valueOf(n.val));
        }
        int currValue = Integer.valueOf(sb.toString());
        result = result + currValue;
    }
 
    return result;
}
 
public void dfs(TreeNode n, ArrayList<TreeNode> l,  ArrayList<ArrayList<TreeNode>> all){
    if(n.left==null && n.right==null){
        ArrayList<TreeNode> t = new ArrayList<TreeNode>();
        t.addAll(l);
        all.add(t);
    }
 
    if(n.left!=null){
        l.add(n.left);
        dfs(n.left, l, all);
        l.remove(l.size()-1);
    }
 
    if(n.right!=null){
        l.add(n.right);
        dfs(n.right, l, all);
        l.remove(l.size()-1);
    }
 
}

Same approach, but simpler coding style.

public int sumNumbers(TreeNode root) {
    if(root == null) 
        return 0;
 
    return dfs(root, 0, 0);
}
 
public int dfs(TreeNode node, int num, int sum){
    if(node == null) return sum;
 
    num = num*10 + node.val;
 
    // leaf
    if(node.left == null && node.right == null) {
        sum += num;
        return sum;
    }
 
    // left subtree + right subtree
    sum = dfs(node.left, num, sum) + dfs(node.right, num, sum);
    return sum;
}

If you want someone to read your code, please put the code inside <pre><code> and </code></pre> tags. For example:

<pre><code> 
String foo = "bar";
</code></pre>

Alik Elzin

You can present the code much prettier using:

code goes here“
Alik Elzin

I might have a simpler approach – without passing the sum – just the number we built so far.

int sumRootToLeaf(Node root) { if (root == null) return 0;
return sumRootToLeaf(root, 0) } int sumNodeToLeaf(Node node, int num) { num = num * 10 + node.val; // Leaf if (node.left == null && node.right == null) { return num; } int sum = 0; if (node.left != null) { sum += sumNodeToLeaf(node.left, num); } if (node.right != null) { sum += sumNodeToLeaf(node.right, num); }
return sum; }
Rahul Manghnani

A video explanation – https://youtu.be/x2JWKKx1ywk
Warren Zhang

Your code has bug, instead of using:

int currValue = Integer.valueOf(sb.toString());

You should use:

int currValue = Integer.parseInt(sb.toString(), 2);
Huthayfa Ainqawi

You don’t need extra space

/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
import java.lang.Integer;

class Solution {
public int sumNumbers(TreeNode root) {

if (root == null) return 0;

return sumNumbers(0, “”, root);
}

public int sumNumbers(int sum, String path, TreeNode root) {

if (root.left == null && root.right == null) {
return sum += Integer.parseInt(path + root.val);
}

if (root.left != null) {
sum = sumNumbers(sum, path + root.val , root.left);
}

if (root.right != null) {
sum = sumNumbers(sum, path + root.val , root.right);
}

return sum;
}
}
Muneza Gntl

My version of this:

public static int temp_sum= 0;
public static void dfs(TreeNode root, int sum){
if (root == null) return ;

if (root.left != null)
sum += root.data*10 + root.left.data;

if(root.right != null)
sum += root.data*10 + root.right.data;

if (sum > temp_sum) //only keep max sum during back track of call functions
temp_sum = sum;

dfs(root.left,sum);
dfs(root.right, sum);
}
Nada Abo ElSeod

Why do we need to have num and sum as parameters? this code below should just work:

int sumTree(TreeNode* node, int curSum)
{
if(!node)
return 0;

curSum = (curSum * 10) + node->val;
if(isLeafNode(node))
return curSum;

return sumTree(node->left, curSum) + sumTree(node->right, curSum);

}
Juan Carlos Nuño

Better BFS solution, using only one queue:

public int sumNumbers(TreeNode root) { if (root == null) return 0;
int sum = 0; Queue q = new LinkedList(); q.offer(root); while (!q.isEmpty()) { TreeNode temp = q.poll(); if (temp.left == null && temp.right == null) sum += temp.val; int num = (temp.val * 10); if (temp.left != null) { temp.left.val = temp.left.val + num; q.offer (temp.left); } if (temp.right != null) { temp.right.val = temp.right.val + num; q.offer(temp.right); } } return sum;
}
Madhumitha

Post order travesal+addition logics

import java.util.Stack;

public class sumToLeaf {

public static void main(String[] args) {

TreeNode t = new TreeNode(1);

t.left = new TreeNode(2);

t.right = new TreeNode(3);

t.left.left = new TreeNode(4);

t.left.right = new TreeNode(5);

t.left.right.left = new TreeNode(6);

int s=sum2Leaf(t);

System.out.println(s);

}

private static int sum2Leaf(TreeNode root)

{

Stack stack = new Stack();

stack.push(root);

TreeNode prev = null;

int num=root.val,sum=0;

int temp=0;

while(!stack.empty()){

TreeNode curr = stack.peek();

if(prev == null || prev.left == curr || prev.right == curr)

{

if(curr.left != null)

{

num=(num*10)+curr.left.val;

stack.push(curr.left);

}

else if(curr.right != null)

{

sum+=num;

temp=stack.peek().val;

num=num-temp+curr.right.val;

stack.push(curr.right);

}

else

{

sum+=num;

temp= stack.pop().val;

num=num-temp;

}

}

else if(curr.left == prev)

{

if(curr.right != null)

{

num=num+curr.right.val;

stack.push(curr.right);

}else

{

temp= stack.pop().val;

num=(num-(temp*10))/10;

}

}

else if(curr.right == prev)

{

temp= stack.pop().val;

num=(num-(temp*10))/10;

}

prev = curr;

}

return sum;

}

}
disqus_t359ByPNg8

Solution using BFS !

An Iterative Solution !

public int sumNumbers(TreeNode root) {

if(root == null){
return 0;

}
int sum =0;
LinkedList queue = new LinkedList();
LinkedList sumQueue = new LinkedList();

queue.add(root);
sumQueue.add(root.val);
while(queue.isEmpty() == false){

TreeNode temp = queue.poll();
int tempSum = sumQueue.poll();

if(temp.left == null && temp.right == null){
sum = sum + tempSum;
}

if(temp.left!=null){

queue.add(temp.left);
sumQueue.add(tempSum*10+ temp.left.val);

}

if(temp.right != null){
queue.add(temp.right);
sumQueue.add(tempSum *10 + temp.right.val);

}

}

return sum;
}
Karim El Shabrawy

Hi,

I think I get a better solution :

public int sumNumbers(TreeNode root) { return sumNumbers(root, 0); } public int sumNumbers(TreeNode root, int current) { if (root == null) return 0; if (root.left == null && root.right == null) return root.val+current*10; current = current*10 + root.val; return sumNumbers(root.left, current)+sumNumbers(root.right, current); }

What do you think ?

BR,

Karim El Shabrawy
[email protected]

LeetCode – Sum Root to Leaf Numbers (Java)

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