Adding k_sum_paths

Author: mandliya

tree_problems/k_sum_paths.cpp

@@ -0,0 +1,105 @@
+/*
+ * Given a binary tree, print all the paths whose sum is equal to k
+ *          1
+ *       /     \
+ *     3        -1
+ *   /   \     /   \
+ *  2     1   4     5                        
+ *       /   / \     \                    
+ *      1   1   2     6
+ *
+ * For k = 5:
+ * 3 2 
+ * 3 1 1 
+ * 1 3 1 
+ * 4 1 
+ * 1 -1 4 1 
+ * -1 4 2 
+ * 5 
+ * 1 -1 5     
+ */
+
+#include <iostream>
+#include <vector>
+
+struct TreeNode
+{
+    int data;
+    TreeNode* left;
+    TreeNode* right;
+    TreeNode(int d) : data {d}, left {nullptr}, right {nullptr} { }
+};
+
+void printPath(const std::vector<int>& path, int index)
+{
+    for (auto it = path.begin() + index; it != path.end(); ++it)
+    {
+        std::cout << *it << " ";
+    }
+    std::cout << std::endl;
+}
+
+void printKPaths(TreeNode * node, std::vector<int>& paths, int k)
+{
+    if (!node)
+    {
+        return;
+    }
+
+    // push the current node to paths
+    //
+    paths.push_back(node->data);
+
+    // now, lets explore the left and right sub-trees
+    //
+    printKPaths(node->left, paths, k);
+    printKPaths(node->right, paths, k);
+
+    // check if we have reached sum of tree nodes to k.
+    // also, do not break, once we have reached k, as we may have negative
+    // values too.
+    //
+    /*
+    int sum = 0;
+    for (int j=paths.size()-1; j>=0; j--)
+    {
+        sum += (paths[j]);
+        if (sum == k)
+        {
+            printPath(paths, j);
+        }
+    }
+    */
+    int sum = 0;
+    for (auto it = paths.rbegin(); it != paths.rend(); ++it)
+    {
+        sum += (*it);
+        if (sum == k)
+        {
+            int indexFromStart = paths.size() - 1 - (it - paths.rbegin());
+            printPath(paths, indexFromStart);
+        }
+    }
+
+    paths.pop_back();
+}
+
+int main()
+{
+    TreeNode* root = new TreeNode(1);
+    root->left = new TreeNode(3);
+    root->left->left = new TreeNode(2);
+    root->left->right = new TreeNode(1);
+    root->left->right->left = new TreeNode(1);
+    root->right = new TreeNode(-1);
+    root->right->left = new TreeNode(4);
+    root->right->left->left = new TreeNode(1);
+    root->right->left->right = new TreeNode(2);
+    root->right->right = new TreeNode(5);
+    root->right->right->right = new TreeNode(2);
+
+    int k = 5;
+    std::vector<int> paths;
+    printKPaths(root, paths, k);
+    return 0;
+}