Create largestBST_in_binary_tree.cpp

dynamic_programming/largestBST_in_binary_tree.cpp

@@ -0,0 +1,52 @@
+// Tree node structure  used in the program
+
+struct Node {
+    int data;
+    Node *left;
+    Node *right;
+
+    Node(int val) {
+        data = val;
+        left = right = NULL;
+    }
+};
+
+// Return the size of the largest sub-tree which is also a BST
+struct info {
+    int subtree_size;
+    int max;
+    int min;
+    int largestBST_size;
+    bool isBST;
+};
+
+// utility function
+info largestBSTBT(Node *root) {
+    if (!root)
+        return {0, INT_MIN, INT_MAX, 0, true};
+    if (!root->left and !root->right)
+        return {1, root->data, root->data, 1, true};
+
+    info left = largestBSTBT(root->left);
+    info right = largestBSTBT(root->right);
+
+    info sol;
+    sol.subtree_size = (1 + left.subtree_size + right.subtree_size);
+
+    if (left.isBST and right.isBST and left.max < root->data and
+        right.min > root->data) {
+        sol.isBST = true;
+        sol.min = min(left.min, min(right.min, root->data));
+        sol.max = max(right.max, max(left.max, root->data));
+        sol.largestBST_size = sol.subtree_size;
+
+        return sol;
+    }
+
+    sol.largestBST_size = max(left.largestBST_size, right.largestBST_size);
+    sol.isBST = false;
+
+    return sol;
+}
+
+int largestBst(Node *root) { return largestBSTBT(root).largestBST_size; }