Added new Java file MinSubstrContainingChars.java in Java/strings #2011

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AzadN wants to merge 16 commits into TheAlgorithms:master from AzadN:Minimum_Substring_Containing_Said_Characters

strings/MinSubstrContainingChars.java

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+    package strings;
+    import java.util.*;
+    public class MinSubstrContainingChars {
+      public static void main(String[] args) {
+        // Testcases
+        assert smallestSubstrContaining("workforcode", "wfc").equals("workforc");
+        assert smallestSubstrContaining("abcdeklmhactr", "abcl").equals("abcdekl");
+        assert smallestSubstrContaining("SachinTendulkar", "SrT").equals("SachinTendulkar");
+      }
+      // Find the smallest length substring of a string containing all the characters in smaller string
+      public static String smallestSubstrContaining(String bigString, String smallString) {
+        HashMap<Character, Integer> targetCharCounts = getCharCounts(smallString);
+        int[] substrBounds = getSubstringBounds(bigString, targetCharCounts);
+        return getStringFromBounds(bigString, substrBounds);
+      }
+      // Builds HashMap of characters to its counts
+      public static HashMap<Character, Integer> getCharCounts(String str) {
+        HashMap<Character, Integer> charCounts = new HashMap<>();
+        for (char x : str.toCharArray()) {
+          increaseCharCount(x, charCounts);
+        }
+        return charCounts;
+      }
+      // Increase occurrence count of character x in hashmap
+      public static void increaseCharCount(Character x, HashMap<Character, Integer> charCounts) {
+        charCounts.put(x, charCounts.getOrDefault(x, 0) + 1);
+      }
+      // Decrease occurrence count of character x in hashmap
+      public static void decreaseCharCount(char x, HashMap<Character, Integer> charCounts) {
+        charCounts.put(x, charCounts.get(x) - 1);
+      }
+      // Gets the bounds of substring occurrence
+      public static int[] getSubstringBounds(String str, HashMap<Character, Integer> charCounts) {
+        int[] substrBounds = new int[] {0, (int) Double.POSITIVE_INFINITY};
+        HashMap<Character, Integer> substrCharCounts = new HashMap<>();
+        int numUniqueChars = charCounts.size();
+        int numUniqueCharsDone = 0;
+        int left = 0, right = 0;
+        while (right < str.length()) {
+          char rightChar = str.charAt(right);
+          if (!charCounts.containsKey(rightChar)) {
+            right++;
+            continue;
+          }
+          increaseCharCount(rightChar, substrCharCounts);
+          if (substrCharCounts.get(rightChar).equals(charCounts.get(rightChar))) numUniqueCharsDone++;
+          while (numUniqueCharsDone == numUniqueChars && left <= right) {
+            substrBounds = getCloserBounds(left, right, substrBounds[0], substrBounds[1]);
+            char leftChar = str.charAt(left);
+            if (!charCounts.containsKey(leftChar)) {
+              left++;
+              continue;
+            }
+            if (substrCharCounts.get(leftChar).equals(charCounts.get(leftChar))) numUniqueCharsDone--;
+            decreaseCharCount(leftChar, substrCharCounts);
+            left++;
+          }
+          right++;
+        }
+        // System.out.println((int)Double.POSITIVE_INFINITY+" "+Arrays.toString(substrBounds));
+        return substrBounds;
+      }
+      // Find the closer bound out of (index1, index2) and (index3, index4)
+      public static int[] getCloserBounds(int index1, int index2, int index3, int index4) {
+        return (index2 - index1 < index4 - index3)
+            ? new int[] {index1, index2}
+            : new int[] {index3, index4};
+      }
+      // Split string into substring starting from bounds[0] and ending at bounds[1]
+      public static String getStringFromBounds(String str, int[] bounds) {
+        int start = bounds[0], end = bounds[1];
+        if (end == (int) Double.POSITIVE_INFINITY) return "";
+        return str.substring(start, end + 1);
+      }
+    }

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Added new Java file MinSubstrContainingChars.java in Java/strings #2011

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