Update remove_all_adjacent_from_string_ii.cpp

Author: avidLearnerInProgress

remove_all_adjacent_from_string_ii.cpp

@@ -1,48 +1,81 @@
-class Solution {
-private:
-    void removeHelper(string &s, int K) {
-        int n = s.length();
-        if(n < K ) return; // edgecase
-		// cout<<"\nCurrent string - "<<s<<"\n";
+// class Solution {
+// private:
+//     void removeHelper(string &s, int K) {
+//         int n = s.length();
+//         if(n < K ) return; // edgecase
+// 		// cout<<"\nCurrent string - "<<s<<"\n";
 
-		bool remove = false;
-        int position = 0;
-        int start = 0;
+// 		bool remove = false;
+//         int position = 0;
+//         int start = 0;
 
-        while(position <= n-K+1) {
-            if(s[position] == s[position+1]) { // if two characters match, then check for the next K characters
-                start = position; // initialize start pointer for removal
-                // cout<<"Start"<<start<<"\t";
-                int checkEqual = 1; // to check for K matches, the count of equal matches must be K - 1. Thus, 1 + K - 1 = K.
-                while(s[position] == s[position+1]) { // if all the next K characters match
-                    ++position, ++checkEqual;
-                    if(checkEqual == K) break; 
-                }
-                // cout<<"CheckEqual"<<checkEqual<<"\n";
-                if(checkEqual == K and start <= n-K) {
-                    remove = true; // flag for recursive call
-                    s.erase(s.begin() + start, s.begin() + start + K);
-                    cout<<s<<" |##| "<<remove<<" | ";
-                    position += K;
-                    if(position == n) { // check for out of bounds
-                        // cout<<"1\n";
-                        break;
-                    }
-                    else
-                        // cout<<"0\n";
+//         while(position <= n-K+1) {
+//             if(s[position] == s[position+1]) { // if two characters match, then check for the next K characters
+//                 start = position; // initialize start pointer for removal
+//                 // cout<<"Start"<<start<<"\t";
+//                 int checkEqual = 1; // to check for K matches, the count of equal matches must be K - 1. Thus, 1 + K - 1 = K.
+//                 while(s[position] == s[position+1]) { // if all the next K characters match
+//                     ++position, ++checkEqual;
+//                     if(checkEqual == K) break; 
+//                 }
+//                 // cout<<"CheckEqual"<<checkEqual<<"\n";
+//                 if(checkEqual == K and start <= n-K) {
+//                     remove = true; // flag for recursive call
+//                     s.erase(s.begin() + start, s.begin() + start + K);
+//                     cout<<s<<" |##| "<<remove<<" | ";
+//                     position += K;
+//                     if(position == n) { // check for out of bounds
+//                         // cout<<"1\n";
+//                         break;
+//                     }
+//                     else
+//                         // cout<<"0\n";
+//                 }
+//             }
+//             else {
+//                 ++position; //increment and check next char in case of mismatch
+//             }
+//         }
+//         if(remove == false) return; //if no duplicate found or if string has become empty after recursive deletions
+//         else if(remove == true) removeHelper(s, K);
+//     }
+// public:
+//     string removeDuplicates(string S, int k) {
+//         if(S == "") return "";
+//         removeHelper(S, k);
+//         return S;   
+//     }  
+// };
+
+
+
+//stack based solution
+class Solution {
+public:
+    string removeDuplicates(string s, int k) {
+        stack<pair<int,int>> st;//stack will hold  (index, number of same character before the index including itself)
+        
+        for(int i = 0; i < s.size(); i++) {
+            if(!st.empty() and s[st.top().first] == s[i]) { //if the current character matches with the character in the top of the stack
+                if(st.top().second + 1 == k) { //if adding the current character in list , makes a list of size 'k' of same chatacters ,
+                    int temp = k - 1;
+                    while(temp--) 
+                        st.pop();
                 }
-            }
-            else {
-                ++position; //increment and check next char in case of mismatch
-            }
+                else   //if it doesn't make a size of 'k' then push (index, number of same character) pair
+                    st.push({i,st.top().second + 1});
+            }      
+            else //if the stack is empty , push the current character index and number of same character , which is 1 
+                st.push({i, 1});
+            
+        }
+    
+        string result = "";
+        while(!st.empty()) {
+            result += s[st.top().first];
+            st.pop();
         }
-        if(remove == false) return; //if no duplicate found or if string has become empty after recursive deletions
-        else if(remove == true) removeHelper(s, K);
+        reverse(result.begin(), result.end());
+        return result;
     }
-public:
-    string removeDuplicates(string S, int k) {
-        if(S == "") return "";
-        removeHelper(S, k);
-        return S;   
-    }  
 };