Added solution for distribute coins in binary tree

Author: avidLearnerInProgress

distribute_coins_binary_tree.cpp

@@ -0,0 +1,28 @@
+/**
+ * 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:
+    int helper(TreeNode* root, int &sum) {
+        if(!root) return 0;
+        
+        int l = helper(root->left, sum);
+        int r = helper(root->right, sum);
+        sum += abs(l) + abs(r);
+        return root->val + l + r - 1;
+    }
+    
+    int distributeCoins(TreeNode* root) {
+        int sum = 0;
+        helper(root, sum);
+        return sum;
+    }
+};