Shortest palindrome

Signed-off-by: begeekmyfriend <[email protected]>

Author: begeekmyfriend

214_shortest_palindrome/Makefile

@@ -0,0 +1,2 @@
+all:
+	gcc -O2 -o test shortest_palindrome.c

214_shortest_palindrome/shortest_palindrome.c

@@ -0,0 +1,50 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdbool.h>
+
+static inline char *rev_cpy(char *dst, char *src, int size)
+{
+    while (size-- > 0) {
+        *--dst = *src++;
+    }
+    return dst;
+}
+
+static char *shortestPalindrome(char *s)
+{
+    int i, j, len = strlen(s);
+    char *result = malloc(2 * len + 2);
+
+    strcpy(result, s);
+    result[len] = '#';
+    rev_cpy(result + 2 * len + 1, s, len);
+
+    int res_len = 2 * len + 1;
+    int *next = malloc(res_len * sizeof(int));
+    memset(next, 0, res_len * sizeof(int));
+    for (i = 1; i < res_len; i++) {
+        int j = next[i - 1];
+        while (j > 0 && result[i] != result[j]) {
+            j = next[j - 1];
+        }
+        j += result[i] == result[j];
+        next[i] = j;
+    }
+
+    memmove(result, result + len + 1, len + 1);
+    int start = len - next[res_len - 1];
+    strcpy(result + start, s);
+    return result;
+}
+
+int main(int argc, char **argv)
+{
+    if (argc != 2) {
+        fprintf(stderr, "Usage: ./test string\n");
+        exit(-1);
+    }
+
+    printf("%s\n", shortestPalindrome(argv[1]));
+    return 0;
+}