Create min_window_substring.cpp

Author: avidLearnerInProgress

min_window_substring.cpp

@@ -0,0 +1,53 @@
+class Solution {
+public:
+    string minWindow(string s, string t) {
+        
+        if(s.size() < t.size()) return "";
+        
+        int hashPattern[256] = {0}, hashString[256] = {0};
+        for(auto ch : t) {
+            hashPattern[ch]++;
+        }
+        
+        int count = 0, start = 0, startIndex = -1, minWindowLength = INT_MAX;
+        for(int i=0; i<s.size(); i++) {
+            
+            //increment occurence of char in string_map
+            hashString[s[i]]++;
+            
+            // Here we check if the current char is in the pattern as well. 
+            // Since we calculate running frequency of char in string_map as we encounter in the for loop, we do a <= comparison of hashString[s[i]] and hashPattern[s[i]]. It means the count of current char in string_map should be either equal count of current char in hash_map or less than count of current char in hash_map 
+            //if s[i] is in pattern_map and hashString[s[i]] == hashPattern[s[i]] or  hashString[s[i]] < hashPattern[s[i]]
+            if(hashPattern[s[i]] != 0 and hashString[s[i]] <= hashPattern[s[i]]) {
+                count++;
+            }
+            
+            
+            if(count == t.size()) { //if we find the pattern in the string
+                
+                //minimize the window from start
+                
+                while((hashString[s[start]] > hashPattern[s[start]]) or hashPattern[s[start]] == 0) {
+                    
+                    //if current char at start is occuring more times than in pattern, we can minimize the window.
+                    //remove the current char at start from string_map and increment start; thereby reducing size of window.
+                    if(hashString[s[start]] > hashPattern[s[start]]) hashString[s[start]]--;
+                    
+                    //if the current char at start is not present in the pattern, just increment the start...
+                    start++;
+                }
+                
+                //get the minimum of all the windows seen so far
+                int currentWindowLength = i - start + 1;
+                if(currentWindowLength < minWindowLength) {
+                    minWindowLength = currentWindowLength;
+                    startIndex = start;
+                }
+            }
+        }
+        
+        if(startIndex == -1) return "";
+        else return s.substr(startIndex, minWindowLength);
+        
+    }
+};