source: tests/avltree/avl3.cfa @ c9f4cf8

#include "avl.h"
#include "avl-private.h"
#include <stdlib.hfa>

// swaps the data within two tree nodes
forall(otype K | Comparable(K), otype V)
void node_swap(tree(K, V) * t, tree(K, V) * t2){
        swap( t->key,  t2->key);
        swap( t->value, t2->value);
}

// go left as deep as possible from within the right subtree
forall(otype K | Comparable(K), otype V)
tree(K, V) * find_successor(tree(K, V) * t){
        tree(K, V) * find_successor_helper(tree(K, V) * t){
                // go left as deep as possible, return the last node
                if (empty(t->left)){
                        return t;
                } else {
                        return find_successor_helper(t->left);
                }
        }
        return find_successor_helper(t->right);
}

// cleanup - don't want to deep delete, so set children to NULL first.
forall(otype K | Comparable(K), otype V)
void deleteSingleNode(tree(K, V) * t) {
        t->left = NULL;
        t->right = NULL;
        delete(t);
}

// does the actual remove operation once we've found the node in question
forall(otype K | Comparable(K), otype V)
tree(K, V) * remove_node(tree(K, V) * t){
        // is the node a leaf?
        if (empty(t->left) && empty(t->right)){
                // yes, just delete this node
                delete(t);
                return NULL;
        } else if (empty(t->left)){
                // if the left is empty, there is only one child -> move right up
                node_swap(t, t->right);
                tree(K, V) * tmp = t->right;

                // relink tree
                t->left = tmp->left;
                t->right = tmp->right;

                setParent(t->left, t);
                setParent(t->right, t);
                deleteSingleNode(tmp);
                return t;
        } else if (empty(t->right)){
                // if the right is empty, there is only one child -> move left up
                node_swap(t, t->left);
                tree(K, V) * tmp = t->left;

                // relink tree
                t->left = tmp->left;
                t->right = tmp->right;

                setParent(t->left, t);
                setParent(t->right, t);
                deleteSingleNode(tmp);
                return t;
        } else {
                // swap with the successor
                tree(K, V) * s = find_successor(t);
                tree(K, V) * parent = s->parent;

                if (parent->left == s){
                        parent->left = s->right;
                } else {
                        assert(parent->right == s);
                        parent->right = s->right;
                }
                setParent(s->right, parent);
                node_swap(t, s);
                deleteSingleNode(s);
                return t;
        }
}

// finds the node that needs to be removed
forall(otype K | Comparable(K), otype V)
tree(K, V) * remove_helper(tree(K, V) * t, K key, int * worked){
        if (empty(t)){
                // did not work because key was not found
                // set the status variable and return
                *worked = 1;
        } else if (t->key == key) {
                t = remove_node(t);
        } else if (t->key < key){
                t->right = remove_helper(t->right, key, worked);
        } else {
                // t->key > key
                t->left = remove_helper(t->left, key, worked);
        }
        // try to fix after deleting
        if (! empty(t)) {
                t = tryFix(t);
        }
        return t;
}

forall(otype K | Comparable(K), otype V)
int remove(tree(K, V) ** t, K key){
        int worked = 0;
        tree(K, V) * newTree = remove_helper(*t, key, &worked);
        *t = newTree;
        return worked;
}

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