From 56a878c5eb663f60b33d9e9c294d8c007df1c466 Mon Sep 17 00:00:00 2001
From: Sabyasachi <43935997+sabrajsab@users.noreply.github.com>
Date: Fri, 16 Oct 2020 15:45:31 +0530
Subject: [PATCH] leetcode #28 "implement strStr()"

---
 leetcode/cpp/string/28.cpp | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)
 create mode 100644 leetcode/cpp/string/28.cpp

diff --git a/leetcode/cpp/string/28.cpp b/leetcode/cpp/string/28.cpp
new file mode 100644
index 00000000..ce31afe2
--- /dev/null
+++ b/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);
+    }
+};