Right Rotate

Lesson 7 of 16 in Coddy's AVL Tree - Data Structures Series #10 course.

When a node's left side is too tall, a right rotation fixes it. Call the unbalanced node y and its left child x. The rotation promotes x to take y's place: x becomes the new subtree root, y becomes x's right child, and x's old right subtree (call it T2) is reattached as y's new left child, since every value in T2 is still greater than x and less than y.

After relinking the pointers, both y and x need their height recomputed, y first since it is now lower in the tree.

Challenge

Easy

Write a method rotateRight(y) on AVLTree. Let x = y.left and T2 = x.right. Set x.right = y and y.left = T2, recompute the height of y then x as 1 + max(getHeight(left), getHeight(right)), and return x as the new subtree root.

Try it yourself

#include <stdio.h>
#include <string.h>
#include "avltree.h"

int main(void) {
    AVLTree* tree = AVLTree_create();
    char line[256];
    while (fgets(line, sizeof(line), stdin) != NULL) {
        line[strcspn(line, "\r\n")] = '\0';
        if (strcmp(line, "1") == 0) {
            Node* y = Node_create(30);
            y->height = 3;
            Node* x = Node_create(20);
            x->height = 2;
            Node* t1 = Node_create(10);
            t1->height = 1;
            x->left = t1;
            y->left = x;
            Node* newRoot = AVLTree_rotateRight(tree, y);
            printf("%d %d %d %d\n", newRoot->value, newRoot->height, newRoot->left->value, newRoot->right->value);
        }
        if (strcmp(line, "2") == 0) {
            Node* y = Node_create(50);
            y->height = 3;
            Node* x = Node_create(30);
            x->height = 2;
            x->left = Node_create(20);
            x->left->height = 1;
            x->right = Node_create(40);
            x->right->height = 1;
            y->left = x;
            y->right = Node_create(60);
            y->right->height = 1;
            Node* newRoot = AVLTree_rotateRight(tree, y);
            printf("%d %d %d %d %d %d\n", newRoot->value, newRoot->height, newRoot->left->value, newRoot->right->value, newRoot->right->left->value, newRoot->right->right->value);
        }
    }
    return 0;
}