Left Rotate

Lesson 8 of 16 in Coddy's AVL Tree - Data Structures Series #10 course.

A left rotation is the mirror image of the right rotation you just wrote, used when a node's right side is too tall. Call the unbalanced node x and its right child y. y becomes the new subtree root, x becomes y's left child, and y's old left subtree (T2) is reattached as x's new right child.

Same rule for heights: recompute x first, then y, since x is now the lower node.

Challenge

Easy

Write a method rotateLeft(x) on AVLTree. Let y = x.right and T2 = y.left. Set y.left = x and x.right = T2, recompute the height of x then y, and return y 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* x = Node_create(10);
            x->height = 3;
            Node* y = Node_create(20);
            y->height = 2;
            Node* t2 = Node_create(30);
            t2->height = 1;
            y->right = t2;
            x->right = y;
            Node* newRoot = AVLTree_rotateLeft(tree, x);
            printf("%d %d %d %d\n", newRoot->value, newRoot->height, newRoot->left->value, newRoot->right->value);
        }
        if (strcmp(line, "2") == 0) {
            Node* x = Node_create(20);
            x->height = 3;
            Node* y = Node_create(40);
            y->height = 2;
            y->left = Node_create(30);
            y->left->height = 1;
            y->right = Node_create(50);
            y->right->height = 1;
            x->left = Node_create(10);
            x->left->height = 1;
            x->right = y;
            Node* newRoot = AVLTree_rotateLeft(tree, x);
            printf("%d %d %d %d %d %d\n", newRoot->value, newRoot->height, newRoot->left->value, newRoot->right->value, newRoot->left->left->value, newRoot->left->right->value);
        }
    }
    return 0;
}