Create Path-Sum-II.cpp

Given the root of a binary tree and an integer targetSum, return all root-to-leaf paths where the sum of the node values in the path equals targetSum. Each path should be returned as a list of the node values, not node references.

A root-to-leaf path is a path starting from the root and ending at any leaf node. A leaf is a node with no children.

Author: Vimal2023

10- Recursion & Backtracking/Path-Sum-II.cpp

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+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+ *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
+ * };
+ */
+class Solution {
+public:
+
+    vector<vector<int>> res; //to store final result
+
+    void traverse(TreeNode* root, vector <int> &path, int rem){
+        if(!root) return; //return at NULL
+
+        if(!root->left && !root->right){ //leaf node reached
+            path.push_back(root->val); //do
+            if(rem == root->val) res.push_back(path);
+        //if remaining sum is same as value of root we have valid path
+            path.pop_back(); // undo
+            return;
+        }
+
+        int val = root->val; //subtract the contribution of this value from rem (remaining sum)
+        path.push_back(val); //do
+        traverse(root->left, path, rem-val); //recurse left subtree
+        traverse(root->right, path, rem-val); //recurse right subtree
+        path.pop_back(); //undo
+
+    }
+
+    vector<vector<int>> pathSum(TreeNode* root, int targetSum) {
+        res.clear(); //reset res 
+        if(!root) return res; //if root itself NULL there are no paths
+        vector <int> path; //to store the path
+        traverse(root, path, targetSum);
+        return res;
+    }
+};