3

Author: kedebug

ImplementstrStr/ImplementstrStr.cpp

@@ -1,48 +1,32 @@
 class Solution {
 public:
     char *strStr(char *haystack, char *needle) {
-        // Start typing your C/C++ solution below
-        // DO NOT write int main() function
-        
-        int hays_length = strlen(haystack);
-        int needle_length = strlen(needle);
-        
-        if (hays_length == 0 && needle_length != 0)
-            return NULL;
-        if (hays_length == 0 || needle_length == 0) 
+        int n = strlen(haystack);
+        int m = strlen(needle);
+        if (m == 0) {
             return haystack;
-        
-        int needle_array[needle_length];
-        
-        getPattern(needle, needle_array, needle_length);
-        int pos = KMP(haystack, hays_length, needle, needle_array, needle_length);
-        if (pos != -2)
-            return haystack + pos + 1;
-        else
-            return NULL;
-    }
-    
-    int KMP(const char *source, int lens, const char *pattern, const int p[], int lenp) {
-        int i, j = -1;
-        for (i = 0; i < lens; i++) {
-            while (j != -1 && source[i] != pattern[j+1])
-                j = p[j];
-            if (source[i] == pattern[j+1])
-                j += 1;
-            if (j == lenp - 1) return i - lenp;
         }
-        return -2;
-    }
-    
-    void getPattern(const char *pattern, int p[], int len) {
-        p[0] = -1;
-        int i, j = -1;
-        for (i = 1; i < len; i++) {
-            while (j != -1 && pattern[i] != pattern[j+1])
-                j = p[j];
-            if (pattern[i] == pattern[j+1]) 
-                j += 1;
-            p[i] = j;
+        vector<int> next(m, -1);
+        for (int i = 1, j = -1; i < m; i++) {
+            while (j != -1 && needle[j+1] != needle[i]) {
+                j = next[j];
+            }
+            if (needle[j+1] == needle[i]) {
+                j++;
+            }
+            next[i] = j;
+        }
+        for (int i = 0, j = -1; i < n; i++) {
+            while (j != -1 && needle[j+1] != haystack[i]) {
+                j = next[j];
+            }
+            if (needle[j+1] == haystack[i]) {
+                j++;
+            }
+            if (j == m - 1) {
+                return haystack + i - m + 1;
+            }
         }
+        return NULL;
     }
-};
+};