src/so-5983-2999

Find the K smallest elements in a Binary Search Tree

src/makefile

@@ -250,6 +250,7 @@ SO_DIRECTORIES = \
 	so-5662-1360 \
 	so-5765-5578 \
 	so-5941-2612 \
+	so-5983-2999 \
 	so-6000-9772 \
 	so-6107-2962 \
 	so-6118-1130 \

src/so-5983-2999/.gitignore

@@ -0,0 +1 @@
+bst41

src/so-5983-2999/README.md

@@ -0,0 +1,5 @@
+### Stack Overflow Question 5983-2999
+
+[SO 5983-2999](https://stackoverflow.com/q/59832999) —
+Binary tree - finding K smallest elements
+

src/so-5983-2999/bst41.c

@@ -0,0 +1,95 @@
+/* SO 5983-2999 */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <inttypes.h>
+#include "stderr.h"
+
+typedef struct Tree
+{
+    int key;
+    struct Tree *left;
+    struct Tree *right;
+} Tree;
+
+typedef void (*Printer)(const Tree *node);
+
+static void bst_print_k_smallest(Tree *tree, int k, int *count, Printer print)
+{
+    if (tree->left != 0)
+        bst_print_k_smallest(tree->left, k, count, print);
+    if (*count < k)
+    {
+        (*count)++;
+        print(tree);
+    }
+    if (*count < k && tree->right != 0)
+        bst_print_k_smallest(tree->right, k, count, print);
+}
+
+static void bst_print_node(const Tree *node)
+{
+    if (node != 0)
+    {
+        printf("Node: 0x%.12" PRIXPTR " - key %3d; left = 0x%.12" PRIXPTR
+               ", right = 0x%.12" PRIXPTR "\n",
+               (uintptr_t)node, node->key, (uintptr_t)node->left,
+               (uintptr_t)node->right);
+    }
+}
+
+static Tree *bst_newnode(int key)
+{
+    Tree *node = malloc(sizeof(*node));
+    if (node == 0)
+        err_syserr("failed to allocate %zu bytes of memory: ", sizeof(*node));
+    node->key = key;
+    node->left = node->right = 0;
+    return node;
+}
+
+static Tree *bst_insert(Tree *root, int key)
+{
+    if (root == NULL)
+        root = bst_newnode(key);
+    else if (key < root->key)
+        root->left = bst_insert(root->left, key);
+    else if (key > root->key)
+        root->right = bst_insert(root->right, key);
+    /* else Repeat - ignore */
+    return root;
+}
+
+static void bst_free(Tree *tree)
+{
+    if (tree != 0)
+    {
+        bst_free(tree->left);
+        bst_free(tree->right);
+        free(tree);
+    }
+}
+
+int main(int argc, char **argv)
+{
+    if (argc > 0)
+        err_setarg0(argv[0]);
+
+    Tree *root = NULL;
+    root = bst_insert(root,  8);
+    root = bst_insert(root,  3);
+    root = bst_insert(root, 10);
+    root = bst_insert(root,  1);
+    root = bst_insert(root,  6);
+    root = bst_insert(root, 14);
+    root = bst_insert(root,  4);
+    root = bst_insert(root,  7);
+    root = bst_insert(root, 13);
+
+    int count = 0;
+    bst_print_k_smallest(root, 9, &count, bst_print_node);
+
+    bst_free(root);
+
+    return 0;
+}

src/so-5983-2999/makefile

@@ -0,0 +1,11 @@
+# SO 5983-2999
+
+include ../../etc/soq-head.mk
+
+PROG1 = bst41
+
+PROGRAMS = ${PROG1}
+
+all: ${PROGRAMS}
+
+include ../../etc/soq-tail.mk