[BAEL-2141] - How to check if a string contains all the letters of the alphabet?

algorithms/src/main/java/com/baeldung/algorithms/string/EnglishAlphabetLetters.java

@@ -0,0 +1,35 @@
+package com.baeldung.algorithms.string;
+
+public class EnglishAlphabetLetters {
+
+    public static boolean checkStringForAllTheLetters(String input) {
+        boolean[] visited = new boolean[26];
+
+        int index = 0;
+
+        for (int id = 0; id < input.length(); id++) {
+            if ('a' <= input.charAt(id) && input.charAt(id) <= 'z') {
+                index = input.charAt(id) - 'a';
+            } else if ('A' <= input.charAt(id) && input.charAt(id) <= 'Z') {
+                index = input.charAt(id) - 'A';
+            }
+            visited[index] = true;
+        }
+
+        for (int id = 0; id < 26; id++) {
+            if (!visited[id]) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    public static boolean checkStringForAllLetterUsingStream(String input) {
+        long c = input.toLowerCase().chars().filter(ch -> ch >= 'a' && ch <= 'z').distinct().count();
+        return c == 26;
+    }
+
+    public static void main(String[] args) {
+        checkStringForAllLetterUsingStream("intit");
+    }
+}

algorithms/src/test/java/com/baeldung/algorithms/string/EnglishAlphabetLettersTest.java

@@ -0,0 +1,20 @@
+package com.baeldung.algorithms.string;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class EnglishAlphabetLettersTest {
+
+    @Test
+    void givenString_whenContainsAllCharacter_thenTrue() {
+        String input = "Farmer jack realized that big yellow quilts were expensive";
+        Assertions.assertTrue(EnglishAlphabetLetters.checkStringForAllTheLetters(input));
+    }
+
+    @Test
+    void givenString_whenContainsAllCharacter_thenUsingStreamExpectTrue() {
+        String input = "Farmer jack realized that big yellow quilts were expensive";
+        Assertions.assertTrue(EnglishAlphabetLetters.checkStringForAllLetterUsingStream(input));
+    }
+
+}