#include <stdio.h>
#include <stdlib.h>
struct tree
{ // node struct
int value;
int key;
char color;
struct tree *left;
struct tree *right;
};
typedef struct tree mynode; // move this below declaration for struct tree.
// keeping declarations in the right order does
// a great deal in making code easier to navigate.
//allocate memory, set color, key, value and NULL sons
mynode* red_node_create (int Key, int Value)
{
mynode *p = (mynode *) calloc (1, sizeof (mynode));
p->color = 1;
p->value = Value;
p->key = Key;
p->left = NULL;
p->right = NULL;
return p;
}
// having a proper way to free memory is very important when dealing
// with trees and lists. It would be better if this was not recursive.
// I'll leave this exercise to you. I'm sure you can find examples on
// the Net.
void free_node(mynode* p)
{
if (!p)
return;
free_node(p->left);
free_node(p->right);
free(p);
}
// Rotation only needs 1 parameter: the root node around which
// rotation occurs.
void rightRotate (mynode ** root)
{
if (!root || !*root || !(*root)->left)
{
printf ("bad arguments in myRightRotate()\n");
return;
}
// take left node, make it parent, make old parent the right node
// of new parent, and make right node of old left node the left node
// of old_parent
// using letters as in graphics on this page:
// https://en.wikipedia.org/wiki/Tree_rotation
// these non leaves nodes cannot be NULL
mynode* Q = *root;
mynode* P = Q->left;
// the leaf nodes could be NULL. Only B is needed.
// but A and C are checked in unit test look-alike below.
mynode* A = P->left;
mynode* B = P->right;
mynode* C = Q->right;
// rotate
*root = P;
P->right = Q;
Q->left = B;
#define CHECK_RIGHT_ROTATE // undef as needed.
#ifdef CHECK_RIGHT_ROTATE
// make sure the nodes are in place.
if (P != *root)
printf("RR error. root is not P\n");
if (Q != (*root)->right)
printf("RR error. root->right is not Q\n");
if (A != P->left)
printf("RR error. A is not at P->left\n");
if (B != Q->left)
printf("RR error. B is not at Q->left\n");
if (C != Q->right)
printf("RR error. C is not at Q->right\n");
#endif
}
int main ()
{
// make minimal tree for a proper rotate. root has both left and right node.
// - left node has both left and right leaf nodes, values and 1 and 2
// - node is a leaf node. value 3
mynode *root = red_node_create (0, 0);
root->left = red_node_create (0, 0);
root->left->left = red_node_create(1, 1);
root->left->right = red_node_create(2, 2);
root->right = red_node_create(3, 3);
// before rotate, we should have
// root->left->left: leaf, value 1
// root->left->right: leaf, value 2
// root->right: leaf, value 3
printf ("before: %d %d %d \n", root->left->left->value, root->left->right->value, root->right->value);
rightRotate (&root);
// after rotate, we should have
// root->left: leaf, value 1
// root->right->left: leaf, value 2
// root->right->right: leaf, value 3
printf ("after: %d %d %d \n", root->left->value, root->right->left->value, root->right->right->value);
free_node(root);
return 0;
}
