Implement strstr

Signed-off-by: Leo Ma <[email protected]>

028_implement_strstr/Makefile

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

028_implement_strstr/strstr.c

@@ -0,0 +1,117 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#if 0
+int strStr(char *haystack, char *needle)
+{
+    if (haystack == NULL || needle == NULL) {
+        return -1;
+    }
+
+    int hlen = strlen(haystack);
+    int nlen = strlen(needle);
+
+    /* haystack < needle */
+    if (hlen < nlen) {
+        return -1;
+    }
+
+    if (nlen == 0) {
+        return 0;
+    }
+
+    /* boyer-moore bad character */
+    int i, j;
+    int bad_steps[128];
+    for (i = 0; i < 128; i++) {
+        bad_steps[i] = nlen;
+    }
+
+    for (i = 0; i < nlen; i++) {
+        bad_steps[needle[i]] = nlen - 1 - i;
+    }
+
+    /* boyer-moore good suffix */
+    int *good_steps = malloc(nlen * sizeof(int));
+    for (i = 0; i < nlen; i++) {
+        good_steps[i] = nlen;
+        for (j = i - 1; j >= 0; j--) {
+            if (!memcmp(needle + i, needle + j, nlen - i)) {
+                good_steps[i] = i - j;
+                break;
+            }
+        }
+    }
+
+    char *p = haystack + nlen - 1;
+    char *q = needle + nlen - 1;
+    char *r = p;
+    while (p - haystack < hlen) {
+        int step = 0;
+        for (i = 1; i <= nlen && *p == *q; i++) {
+            if (q == needle) {
+                return p - haystack;
+            }
+            if (good_steps[nlen - i] > step) {
+                step = good_steps[nlen - i];
+            }
+            p--;
+            q--;
+        }
+
+        if (i == 1 && bad_steps[*p] > step) {
+            step = bad_steps[*p];
+        }
+        r += step;
+        p = r;
+        q = needle + nlen - 1;
+    }
+
+    return -1;
+}
+#endif
+
+static int strStr(char *haystack, char *needle)
+{
+    int i, j, found = 1;
+    unsigned int hlen = strlen(haystack);
+    unsigned int nlen = strlen(needle);
+
+    if (nlen == 0) {
+        return 0;
+    }
+
+    /* Brute force */
+    for (i = 0; i < hlen; i++) {
+        if (haystack[i] == needle[0]) {
+	    for (j = 1; j < nlen; j++) {
+                if (i + j < hlen) {
+                    if (haystack[i + j] != needle[j]) {
+                        found = 0;
+                        break;
+                    }
+                } else {
+                    return -1;
+                }
+	    }
+	    if (found) {
+    		return i;
+    	    }
+	}
+	found = 1;
+    }
+
+    return -1;
+}
+
+int main(int argc, char **argv)
+{
+    if (argc != 3) {
+        fprintf(stderr, "Usage: ./test heystack needle\n");
+        exit(-1);
+    }
+
+    printf("%d\n", strStr(argv[1], argv[2]));
+    return 0;
+}