update strStr()

Change-Id: I0afed8005854afe5a4904a7be032bd6acc8e7a4c

Author: applewjg

ImplementstrStr().h

@@ -1,31 +1,90 @@
 /*
- Author:     Annie Kim, [email protected]
- Date:       Apr 9, 2013
- Update:     Jul 19, 2013 (Refactor)
+ Author:     King, [email protected]
+ Date:       Dec 17, 2014
  Problem:    Implement strStr()
  Difficulty: Easy
- Source:     http://leetcode.com/onlinejudge#question_28
+ Source:     https://oj.leetcode.com/problems/implement-strstr/
  Notes:
  Implement strStr().
  Returns a pointer to the first occurrence of needle in haystack, or null if needle is not part of haystack.
 
- Solution: Check in the haystack one by one. If not equal to needle, reset the pointer.
+ Solution: 1. Check in the haystack one by one. If not equal to needle, reset the pointer.(TLE)
+           2. Classice KMP solution.
+           3. Simplified RK Soluiton. Thanks for [wenyuanhust, [email protected]]
  */
-
 class Solution {
 public:
-    char *strStr(char *haystack, char *needle) {
-        while(true)
-        {
-            char *h = haystack, *n = needle;
-            while (*n != '\0' && *h == *n)
-            {
-                h++; 
-                n++;
+    int strStr_1(char *haystack, char *needle) {
+        int sLen = strlen(haystack);
+        const int tLen = strlen(needle);
+        if (tLen == 0) return 0;
+        if(haystack==NULL || needle==NULL || sLen==0) return -1;
+        int i = 0, j =0;
+        while (i < sLen) {
+            j = 0;
+            int k = i;
+            while (j < tLen && haystack[k] == needle[j]) {
+                ++k, ++j;
+            }
+            if (j == tLen) return k - j;
+            ++i;
+        }
+        return -1;
+    }
+    void getNext(char * T, int next[], int n){
+        int i=0, j=-1;
+        next[0]=-1;
+        while(i<n){
+            while(j>-1&&T[j]!=T[i]) j = next[j];
+            i++,j++;
+            if(T[j]==T[i]) next[i]=next[j];
+            else next[i]=j;
+        }
+    }
+    int strStr_2(char *haystack, char *needle) {
+        int sLen = strlen(haystack);
+        const int tLen = strlen(needle);
+        if (tLen == 0) return 0;
+        if(haystack==NULL || needle==NULL || sLen==0) return -1;
+        
+        int next[tLen+1];
+        getNext(needle,next,tLen);
+        
+        int i=0, j=0;
+        while(i<sLen){
+            while(j>-1&&needle[j]!=haystack[i]) j = next[j];
+            i++,j++;
+            if(j==tLen){
+                return i - j;
+            }
+        }
+        return -1;
+    }
+    int strStr_3(char *haystack, char *needle) {
+        if (needle && *needle == '\0') return 0;
+        if (haystack == NULL || needle == NULL || *haystack == '\0') return -1;
+        long long fh = 0, fn = 0;
+        char *n = needle, *tail = haystack, *head = haystack;
+        while (*n) {
+            if (*tail == '0') return -1;
+            fh += *tail;
+            fn += *n;
+            ++n, ++tail;
+        }
+        --tail;
+        while (*tail) {
+            if (fn == fh) {
+                char *pTemp = head,*nTemp = needle;
+                while (*nTemp && *nTemp == *pTemp) {
+                    ++nTemp; ++pTemp;
+                }
+                if (*nTemp == '\0') return head - haystack;
             }
-            if (*n == '\0') return haystack;
-            if (*h == '\0') return NULL;
-            haystack++;
+            fh -= *head;
+            ++tail;
+            ++head;
+            fh += *tail;
         }
+        return -1;
     }
-};
+};