Fifth update on iterators - HEAP

examples/heap/iterator.c

@@ -0,0 +1,181 @@
+/**
+ * iterator.c
+ *
+ * Creation Date: 15/05/2019
+ *
+ * Authors:
+ * Leonardo Vencovsky (https://github.com/LeoVen)
+ *
+ * Iterator Example
+ */
+#include "heap.h"
+#include <stdio.h>
+#include <inttypes.h>
+
+// Int compare function
+int intcmp(int a, int b)
+{
+    return a - b;
+}
+
+// Creates a heap of integers
+HEAP_GENERATE(h, heap, /* FMOD */, int)
+
+int main(int argc, char const *argv[])
+{
+    // Create a new max heap with an initial capacity of 100
+    heap *my_heap = h_new(100, MaxHeap, intcmp);
+
+    // Add elements to the heap
+    for (int i = 0; i < 20; i++)
+    {
+        h_insert(my_heap, i);
+    }
+
+    // Iterate from the start (index 0) to the end (index count - 1) of the heap
+    for (heap_iter it = my_heap->it_start(my_heap); // Initialize iterator 'it' to the start of the heap
+         !h_iter_end(&it);                          // Conditional stop (until it is not at the end)
+         h_iter_next(&it))                          // Iterator goes one position forward
+    {
+        // Access the current element
+        int e = h_iter_value(&it);
+
+        // Access the current index (index is relative to all the elements in the iteration)
+        size_t i = h_iter_index(&it);
+
+        // Print heap
+
+        // Index is useful in situations like this
+        // If it is the first element
+        if (i == 0)
+            printf("[ %d, ", e);
+        // If it is the last element
+        else if (i == h_count(my_heap) - 1)
+            printf("%d ]\n", e);
+        // For elements at the middle
+        else
+            printf("%d, ", e);
+    }
+
+    // Index can also be used to iterate over a certain portion of a collection
+    size_t limit = h_count(my_heap) / 2;
+    for (heap_iter it = my_heap->it_start(my_heap); !h_iter_end(&it); h_iter_next(&it))
+    {
+        // Access the current element
+        int e = h_iter_value(&it);
+
+        // Access the current index (index is relative to all the elements in the iteration)
+        size_t i = h_iter_index(&it);
+
+        // Print heap up until limit
+
+        // If it is the first element
+        if (i == 0)
+            printf("[ %d, ", e);
+        // If it is the last element
+        else if (i == limit - 1) // -1 because index is 0 based and we want half of the heap
+        {
+            printf("%d ]\n", e);
+            break;
+        }
+        // For elements at the middle
+        else
+            printf("%d, ", e);
+    }
+
+    // Going backwards
+    for (heap_iter it = my_heap->it_end(my_heap); // Initialize iterator 'it' to the end of the heap
+         !h_iter_start(&it);                      // Conditional stop (until it is not at the start)
+         h_iter_prev(&it))                        // Iterator goes one position backwards
+    {
+        // Access the current element
+        int e = h_iter_value(&it);
+
+        // Access the current index (index is relative to all the elements in the iteration)
+        size_t i = h_iter_index(&it);
+
+        // Print heap
+        // Note how the conditions for the first and last elements are simply swapped
+        // Because iterating backwards make the first element be the index count - 1
+        // and the last one be the index 0
+
+        // If it is the first element
+        if (i == h_count(my_heap) - 1)
+            printf("[ %d, ", e);
+        // If it is the last element
+        else if (i == 0)
+            printf("%d ]\n", e);
+        // For elements at the middle
+        else
+            printf("%d, ", e);
+    }
+
+    // You can also use iterators in a while loop
+    // But to do so you must declare the iterator struct outside the loop first
+    heap_iter it;
+
+    // You have three options:
+    // - Initialize it using the functions provided by the heap [ my_heap->it_start() and my_heap->it_end() ]
+    // - Initialize it using the init() function (when the iterator is already allocated)
+    // - Initialize it using the new() function (allocates on the heap, pointers only)
+
+    it = my_heap->it_start(my_heap);
+    it = my_heap->it_end(my_heap);
+
+    // This is equivalent to it_start()
+    h_iter_init(&it, my_heap);
+
+    // For pointers
+    // Also equivalent to it_start()
+    heap_iter *iter = h_iter_new(my_heap);
+
+    // The actual while loop
+    while (!h_iter_end(iter))
+    {
+        // Accessing elements
+        int e = h_iter_value(iter);
+        size_t i = h_iter_index(iter);
+
+        // Print index and element
+        printf("heap[%2" PRIuMAX "] = %2d\n", i, e);
+
+        // Move iterator forwards
+        h_iter_next(iter);
+    }
+
+    // Send the iterator to the start of the heap
+    h_iter_to_start(iter);
+
+    // Send the iterator to the end of the heap
+    h_iter_to_end(iter);
+
+    // Backwards loop
+    while (!h_iter_start(iter))
+    {
+        // Accessing elements
+        int e = h_iter_value(iter);
+        size_t i = h_iter_index(iter);
+
+        // Print index and element
+        printf("heap[%2" PRIuMAX "] = %2d\n", i, e);
+
+        // Move iterator backwards
+        h_iter_prev(iter);
+    }
+
+    // Certain iterators also allow you to modify the contents it is iterating over
+    // Exceptions are collections that depend of the current state of the element
+    // like tree-based collections and heap (collections that have some kind of ordering).
+    // You also can't change the keys of an associative collection
+
+    // In the case of a heap this is not possible because the heap have its
+    // elements ordered. Changing them could cause the heap to be in an invalid
+    // state.
+
+    // Dispose the iterator called by h_iter_new()
+    h_iter_free(iter);
+    // Dispose the heap created
+    h_free(my_heap);
+
+    return 0;
+}

examples/iterators/heap.c

@@ -20,12 +20,9 @@ HEAP_GENERATE(h, heap, static, int)
 
 int main(int argc, char const *argv[])
 {
-    size_t i;
-    int r;
-
     // Initialize heap and add some elements
-    heap *h = h_new(10, MinHeap, intcmp);
-    for (int i = 9; i >= 0; i--)
+    heap *h = h_new(10, MaxHeap, intcmp);
+    for (int i = 0; i < 10; i++)
         h_insert(h, i);
 
     // Initialize iterator
@@ -35,26 +32,30 @@ int main(int argc, char const *argv[])
     // Make the iterator go back and forward
     for (int j = 0; j < 4; j++)
     {
-        while (h_iter_next(&iter, &r, &i))
-            printf("C[%2d] = %2d\n", i, r);
+        while (!h_iter_end(&iter))
+        {
+            printf("C[%2d] = %2d\n", h_iter_index(&iter), h_iter_value(&iter));
+            h_iter_next(&iter);
+        }
         printf("\n");
-        while (h_iter_prev(&iter, &r, &i))
-            printf("C[%2d] = %2d\n", i, r);
+        while (!h_iter_start(&iter))
+        {
+            printf("C[%2d] = %2d\n", h_iter_index(&iter), h_iter_value(&iter));
+            h_iter_prev(&iter);
+        }
         printf("\n\n");
     }
 
-    for (h_iter_tostart(&iter); !h_iter_end(&iter); /**/)
+    for (h_iter_to_start(&iter); !h_iter_end(&iter); h_iter_next(&iter))
     {
-        h_iter_next(&iter, &r, &i);
-        printf("H[%2d] = %2d\n", i, r);
+        printf("H[%2d] = %2d\n", h_iter_index(&iter), h_iter_value(&iter));
     }
 
     printf("\n");
 
-    for (h_iter_toend(&iter); !h_iter_start(&iter); /**/)
+    for (h_iter_to_end(&iter); !h_iter_start(&iter); h_iter_prev(&iter))
     {
-        h_iter_prev(&iter, &r, &i);
-        printf("H[%2d] = %2d\n", i, r);
+        printf("H[%2d] = %2d\n", h_iter_index(&iter), h_iter_value(&iter));
     }
 
     h_free(h);