LeetCode – Path Sum II (Java)

Category: Algorithms >> Interview May 16, 2014

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

the method returns the following:

[
   [5,4,11,2],
   [5,8,4,5]
]

Analysis

This problem can be converted to be a typical depth-first search problem. A recursive depth-first search algorithm usually requires a recursive method call, a reference to the final result, a temporary result, etc.

Java Solution

public List<ArrayList<Integer>> pathSum(TreeNode root, int sum) {
    ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
    if(root == null) 
        return result;
 
    ArrayList<Integer> l = new ArrayList<Integer>();
    l.add(root.val);
    dfs(root, sum-root.val, result, l);
    return result;
}
 
public void dfs(TreeNode t, int sum, ArrayList<ArrayList<Integer>> result, ArrayList<Integer> l){
    if(t.left==null && t.right==null && sum==0){
        ArrayList<Integer> temp = new ArrayList<Integer>();
        temp.addAll(l);
        result.add(temp);
    }
 
    //search path of left node
    if(t.left != null){
        l.add(t.left.val);
        dfs(t.left, sum-t.left.val, result, l);
        l.remove(l.size()-1);
    }
 
    //search path of right node
    if(t.right!=null){
        l.add(t.right.val);
        dfs(t.right, sum-t.right.val, result, l);
        l.remove(l.size()-1);
    }
}

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>

Saravana

public LinkedList<LinkedList> rootToLeafSum(BTNode root, int sum) { if (root == null) return null; LinkedList<LinkedList> paths = new LinkedList(); LinkedList currentPath = new LinkedList(); rootToLeafSum(root, paths, currentPath, sum - root.data); return paths; }
@SuppressWarnings("unchecked") private void rootToLeafSum(BTNode node, LinkedList<LinkedList> paths, LinkedList path, int sum) { if (node.right == null && node.left == null && sum == 0) { path.add(node); paths.add(path); return; } path.add(node); if (node.left != null) { rootToLeafSum(node.left, paths, (LinkedList) path.clone(), sum - node.left.data); } if (node.right != null) { rootToLeafSum(node.right, paths, (LinkedList) path.clone(), sum - node.right.data); } }
niranjan mohan

public boolean hasPathSum(TreeNode root, int sum) {
if(root ==null){
return false;
}
boolean hasSum = sumHelper(root,0,sum);
return hasSum;
}

public boolean sumHelper(TreeNode node,int runningSum,int sum){
if(node ==null){
return false;
}
if(node.left == null && node.right ==null){
runningSum+=node.val;
return (runningSum == sum);
}
runningSum += node.val;
return sumHelper(node.left,runningSum,sum) || sumHelper(node.right,runningSum,sum);
}
Nada Abo ElSeod

Here is my solution:

void findPaths(Node* root, int sum, vector cur, vector<vector>& results)
{
if(root == NULL) return ;

cur.push_back(root->val);

if(root->val == sum && root->left == NULL && root->right == NULL)
{ results.push_back(cur); return ;}

findPaths(root->left, sum-root->val, cur, results);
findPaths(root->right, sum-root->val, cur, results);

}
Mandy Lin

I wrote a solution but it was wrong. Someone could help?

/**

* Definition for a binary tree node.

* public class TreeNode {

* int val;

* TreeNode left;

* TreeNode right;

* TreeNode(int x) { val = x; }

* }

*/

public class Solution {

public List<List> pathSum(TreeNode root, int sum) {

List<List> list = new ArrayList();

List sublist = new ArrayList();

Record record = new Record(0, sublist);

record = DFS(root, sum, record);

if(record.hasPath()) {

list.add(record.getList());

}

return list;

}

public Record DFS(TreeNode node, int sum, Record record) {

if(node == null) {

return null;

}

if(node.left == null && node.right == null) {

if(record.getVal() + node.val == sum) {

record.hasPath();

record.add(node.val);

return record;

} else {

return record;

}

}

record.hasPath();

record.add(node.val);

record.updateVal(node.val);

return (DFS(node.left, sum, record) || DFS(node.right, sum, record));

//return DFS(node.left, sum, record);

}

}

class Record {

private int calculatedVal;

private List sublist;

private boolean foundPath;

public Record(int c, List s) {

this.calculatedVal = c;

this.sublist = s;

this.foundPath = false;

}

public int getVal() {

return calculatedVal;

}

public void updateVal(int val) {

calculatedVal += val;

}

public List getList() {

return sublist;

}

public void add(int val) {

sublist.add(val);

}

public boolean hasPath() {

foundPath = true;

return foundPath;

}

}
Burhan COKCA

It still can be solved with bfs. By using the Path Sum solution, you will need extra list collections and a queue to store the lists while you traversing

public class Solution {
public List<List> pathSum(TreeNode root, int sum) {
List<List> result = new ArrayList<List>();
if(root == null) return result;
LinkedList nodes = new LinkedList();
LinkedList sumValues = new LinkedList();

nodes.add(root);
sumValues.add(root.val);

LinkedList<List> l = new LinkedList<List>();
List a = new ArrayList();
a.add(root.val);
l.add(a);

while(!nodes.isEmpty()){

Integer sumValue = sumValues.poll();
TreeNode t = nodes.poll();
a = l.poll();

if(t.left == null && t.right == null && sumValue == sum){
result.add(a);
}
else{
if(t.right != null) {
nodes.add(t.right);
sumValues.add(t.right.val + sumValue);
List r = new ArrayList();
r.addAll(a);
r.add(t.right.val);
l.add(r);
}

if(t.left != null) {
nodes.add(t.left);
sumValues.add(t.left.val + sumValue);
List le = new ArrayList();
le.addAll(a);
le.add(t.left.val);
l.add(le);
}
}
}
return result;
}
}

LeetCode – Path Sum II (Java)

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