leetcode larissalages#28 "implement strStr()"

leetcode/cpp/string/28.cpp

@@ -0,0 +1,28 @@
+class Solution {
+public:
+    int strStr(string haystack, string needle) {
+        if(needle=="")
+            return 0;
+        double needle_hash=0, hay_hash=0;
+        for(int i=0;i<needle.size();++i)
+        {
+            needle_hash+=((needle[i]-'a')*pow(3,i));
+        }
+        for(int i=0;i<needle.size();++i)
+        {
+            hay_hash+=((haystack[i]-'a')*pow(3,i));
+        }
+        int k=0;
+        do
+        {
+            if(needle_hash==hay_hash)
+                return k;
+            if(k+needle.size()>haystack.size())
+                return -1;
+            hay_hash-=(haystack[k]-'a');
+            hay_hash/=3;
+            hay_hash+=((haystack[k+needle.size()]-'a')*pow(3,needle.size()-1));
+            k++;
+        }while(1);
+    }
+};