solves substrings with distinct characters

Author: anishLearnsToCode

Diff for: README.md

@@ -453,7 +453,7 @@
 | 1859 | [Sorting the Sentence](https://leetcode.com/problems/sorting-the-sentence)                                                                                |                                                               [![Java](assets/java.png)](src/SortingTheSentence.java)                                                                |                                                                                                                                   |
 | 1863 | [Sum of All Subset XOR Totals](https://leetcode.com/problems/sum-of-all-subset-xor-totals)                                                                |                                                             [![Java](assets/java.png)](src/SumOfAllSubsetXORTotals.java)                                                             |                                                                                                                                   |
 | 1869 | [Longer Contiguous Segments of Ones than Zeros](https://leetcode.com/problems/longer-contiguous-segments-of-ones-than-zeros)                              |                                                     [![Java](assets/java.png)](src/LongerContiguousSegmentOfOnesThanZeros.java)                                                      |                                                                                                                                   |
-| 1876 | [Substrings of Size Three with Distinct Characters](https://leetcode.com/problems/substrings-of-size-three-with-distinct-characters)                      |                                                                                                                                                                                      |                                                                                                                                   |
+| 1876 | [Substrings of Size Three with Distinct Characters](https://leetcode.com/problems/substrings-of-size-three-with-distinct-characters)                      |                                                   [![Java](assets/java.png)](src/SubstringsOfSizeThreeWithDistinctCharacters.java)                                                   |                                                                                                                                   |
 | 1880 | [Check if Word Equals Summation of Two Words](https://leetcode.com/problems/check-if-word-equals-summation-of-two-words)                                  |                                                                                                                                                                                      |                                                                                                                                   |
 | 1886 | [Determine Whether Matrix Can Be Obtained By Rotation](https://leetcode.com/problems/determine-whether-matrix-can-be-obtained-by-rotation)                |                                                                                                                                                                                      |                                                                                                                                   |
 | 1893 | [Check if All the Integers in a Range Are Covered](https://leetcode.com/problems/check-if-all-the-integers-in-a-range-are-covered)                        |                                                                                                                                                                                      |                                                                                                                                   |

Diff for: src/SubstringsOfSizeThreeWithDistinctCharacters.java

@@ -0,0 +1,34 @@
+// https://leetcode.com/problems/substrings-of-size-three-with-distinct-characters
+// T: O(N)
+// S: O(1)
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class SubstringsOfSizeThreeWithDistinctCharacters {
+    public int countGoodSubstrings(String s) {
+        if (s.length() < 3) return 0;
+        final Map<Character, Integer> frequency = getFrequency(s, 3);
+        int goodSubStrings = 0;
+        if (frequency.size() == 3) goodSubStrings++;
+        for (int index = 3 ; index < s.length() ; index++) {
+            remove(frequency, s.charAt(index - 3));
+            frequency.put(s.charAt(index), frequency.getOrDefault(s.charAt(index), 0) + 1);
+            if (frequency.size() == 3) goodSubStrings++;
+        }
+        return goodSubStrings;
+    }
+
+    private Map<Character, Integer> getFrequency(String s, int upto) {
+        final Map<Character, Integer> frequencies = new HashMap<>();
+        for (int i = 0 ; i < upto ; i++) {
+            frequencies.put(s.charAt(i), frequencies.getOrDefault(s.charAt(i), 0) + 1);
+        }
+        return frequencies;
+    }
+
+    private void remove(Map<Character, Integer> frequencies, char c) {
+        if (frequencies.get(c) == 1) frequencies.remove(c);
+        else frequencies.put(c, frequencies.get(c) - 1);
+    }
+}