diff --git a/2023/1/2.c b/2023/1/2.c
index 62335dd..23139b7 100644
--- a/2023/1/2.c
+++ b/2023/1/2.c
@@ -1,3 +1,5 @@
+#include "../../util.h"
+
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
@@ -7,28 +9,6 @@ typedef struct {
     char* value;
 } number;
 
-void replace(char *target, const char *needle, const char *replacement)
-{
-    char buffer[1024] = { 0 };
-    char *insert_point = &buffer[0];
-    const char *tmp = target;
-    size_t needle_len = strlen(needle);
-    size_t repl_len = strlen(replacement);
-    while (1) {
-        const char *p = strstr(tmp, needle);
-        if (p == NULL) { // walked past last occurrence of needle; copy remaining part
-            strcpy(insert_point, tmp);
-            break;
-        }
-        memcpy(insert_point, tmp, p - tmp); // copy part before needle
-        insert_point += p - tmp;
-        memcpy(insert_point, replacement, repl_len); // copy replacement string
-        insert_point += repl_len;
-        tmp = p + needle_len;
-    }
-    strcpy(target, buffer);
-}
-
 int main() {
     FILE *inputfile = fopen("./input", "r");
     char *line = malloc(sizeof(char) * 100);
diff --git a/2023/2/1.c b/2023/2/1.c
index 6937989..920465d 100644
--- a/2023/2/1.c
+++ b/2023/2/1.c
@@ -1,3 +1,5 @@
+#include "../../util.h"
+
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
@@ -10,72 +12,6 @@ typedef struct {
     int colors[3];
 } game;
 
-char** str_split(char* a_str, const char a_delim)
-{
-    char** result    = 0;
-    size_t count     = 0;
-    char* tmp        = a_str;
-    char* last_comma = 0;
-    char delim[2];
-    delim[0] = a_delim;
-    delim[1] = 0;
-    /* Count how many elements will be extracted. */
-    while (*tmp)
-    {
-        if (a_delim == *tmp)
-        {
-            count++;
-            last_comma = tmp;
-        }
-        tmp++;
-    }
-    /* Add space for trailing token. */
-    count += last_comma < (a_str + strlen(a_str) - 1);
-    /* Add space for terminating null string so caller
-       knows where the list of returned strings ends. */
-    count++;
-    result = malloc(sizeof(char*) * count);
-    if (result)
-    {
-        size_t idx  = 0;
-        char* token = strtok(a_str, delim);
-        while (token)
-        {
-            assert(idx < count);
-            *(result + idx++) = strdup(token);
-            token = strtok(0, delim);
-        }
-        assert(idx == count - 1);
-        *(result + idx) = 0;
-    }
-    return result;
-}
-
-// Note: This function returns a pointer to a substring of the original string.
-// If the given string was allocated dynamically, the caller must not overwrite
-// that pointer with the returned value, since the original pointer must be
-// deallocated using the same allocator with which it was allocated.  The return
-// value must NOT be deallocated using free() etc.
-char *trimwhitespace(char *str)
-{
-  char *end;
-
-  // Trim leading space
-  while(isspace((unsigned char)*str)) str++;
-
-  if(*str == 0)  // All spaces?
-    return str;
-
-  // Trim trailing space
-  end = str + strlen(str) - 1;
-  while(end > str && isspace((unsigned char)*end)) end--;
-
-  // Write new null terminator character
-  end[1] = '\0';
-
-  return str;
-}
-
 int main() {
     FILE *inputfile = fopen("./input", "r");
     char line[1024] = { 0 };
diff --git a/2023/2/2.c b/2023/2/2.c
index 68f195f..30d7021 100644
--- a/2023/2/2.c
+++ b/2023/2/2.c
@@ -1,3 +1,5 @@
+#include "../../util.h"
+
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
@@ -9,72 +11,6 @@ typedef struct {
     int colors[3];
 } game;
 
-char** str_split(char* a_str, const char a_delim)
-{
-    char** result    = 0;
-    size_t count     = 0;
-    char* tmp        = a_str;
-    char* last_comma = 0;
-    char delim[2];
-    delim[0] = a_delim;
-    delim[1] = 0;
-    /* Count how many elements will be extracted. */
-    while (*tmp)
-    {
-        if (a_delim == *tmp)
-        {
-            count++;
-            last_comma = tmp;
-        }
-        tmp++;
-    }
-    /* Add space for trailing token. */
-    count += last_comma < (a_str + strlen(a_str) - 1);
-    /* Add space for terminating null string so caller
-       knows where the list of returned strings ends. */
-    count++;
-    result = malloc(sizeof(char*) * count);
-    if (result)
-    {
-        size_t idx  = 0;
-        char* token = strtok(a_str, delim);
-        while (token)
-        {
-            assert(idx < count);
-            *(result + idx++) = strdup(token);
-            token = strtok(0, delim);
-        }
-        assert(idx == count - 1);
-        *(result + idx) = 0;
-    }
-    return result;
-}
-
-// Note: This function returns a pointer to a substring of the original string.
-// If the given string was allocated dynamically, the caller must not overwrite
-// that pointer with the returned value, since the original pointer must be
-// deallocated using the same allocator with which it was allocated.  The return
-// value must NOT be deallocated using free() etc.
-char *trimwhitespace(char *str)
-{
-  char *end;
-
-  // Trim leading space
-  while(isspace((unsigned char)*str)) str++;
-
-  if(*str == 0)  // All spaces?
-    return str;
-
-  // Trim trailing space
-  end = str + strlen(str) - 1;
-  while(end > str && isspace((unsigned char)*end)) end--;
-
-  // Write new null terminator character
-  end[1] = '\0';
-
-  return str;
-}
-
 int main() {
     FILE *inputfile = fopen("./input", "r");
     char line[1024] = { 0 };
diff --git a/2023/4/1.c b/2023/4/1.c
index 0b0ac50..a04ff44 100644
--- a/2023/4/1.c
+++ b/2023/4/1.c
@@ -1,3 +1,5 @@
+#include "../../util.h"
+
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
@@ -5,72 +7,6 @@
 #include <stdbool.h>
 #include <assert.h>
 
-char** str_split(char* a_str, const char a_delim)
-{
-    char** result    = 0;
-    size_t count     = 0;
-    char* tmp        = a_str;
-    char* last_comma = 0;
-    char delim[2];
-    delim[0] = a_delim;
-    delim[1] = 0;
-    /* Count how many elements will be extracted. */
-    while (*tmp)
-    {
-        if (a_delim == *tmp)
-        {
-            count++;
-            last_comma = tmp;
-        }
-        tmp++;
-    }
-    /* Add space for trailing token. */
-    count += last_comma < (a_str + strlen(a_str) - 1);
-    /* Add space for terminating null string so caller
-       knows where the list of returned strings ends. */
-    count++;
-    result = malloc(sizeof(char*) * count);
-    if (result)
-    {
-        size_t idx  = 0;
-        char* token = strtok(a_str, delim);
-        while (token)
-        {
-            assert(idx < count);
-            *(result + idx++) = strdup(token);
-            token = strtok(0, delim);
-        }
-        assert(idx == count - 1);
-        *(result + idx) = 0;
-    }
-    return result;
-}
-
-// Note: This function returns a pointer to a substring of the original string.
-// If the given string was allocated dynamically, the caller must not overwrite
-// that pointer with the returned value, since the original pointer must be
-// deallocated using the same allocator with which it was allocated.  The return
-// value must NOT be deallocated using free() etc.
-char *trimwhitespace(char *str)
-{
-  char *end;
-
-  // Trim leading space
-  while(isspace((unsigned char)*str)) str++;
-
-  if(*str == 0)  // All spaces?
-    return str;
-
-  // Trim trailing space
-  end = str + strlen(str) - 1;
-  while(end > str && isspace((unsigned char)*end)) end--;
-
-  // Write new null terminator character
-  end[1] = '\0';
-
-  return str;
-}
-
 int main() {
     FILE *inputfile = fopen("./input", "r");
     char line[2048] = { 0 };
diff --git a/lib/util.c b/lib/util.c
index 7389d9c..8e27738 100644
--- a/lib/util.c
+++ b/lib/util.c
@@ -64,3 +64,25 @@ char *trimwhitespace(char *str)
     end[1] = '\0';
     return str;
 }
+
+void replace(char *target, const char *needle, const char *replacement)
+{
+    char buffer[1024] = { 0 };
+    char *insert_point = &buffer[0];
+    const char *tmp = target;
+    size_t needle_len = strlen(needle);
+    size_t repl_len = strlen(replacement);
+    while (1) {
+        const char *p = strstr(tmp, needle);
+        if (p == NULL) { // walked past last occurrence of needle; copy remaining part
+            strcpy(insert_point, tmp);
+            break;
+        }
+        memcpy(insert_point, tmp, p - tmp); // copy part before needle
+        insert_point += p - tmp;
+        memcpy(insert_point, replacement, repl_len); // copy replacement string
+        insert_point += repl_len;
+        tmp = p + needle_len;
+    }
+    strcpy(target, buffer);
+}
diff --git a/lib/util.h b/lib/util.h
index 1e83966..80f8e32 100644
--- a/lib/util.h
+++ b/lib/util.h
@@ -1,4 +1,3 @@
-
 char** str_split(char* a_str, const char a_delim);
 char* trimwhitespace(char *str);
-
+void replace(char *target, const char *needle, const char *replacement);