Add solution of IsSubsequence task

Author: andrei-punko

src/main/java/by/andd3dfx/string/IsSubsequence.java

@@ -0,0 +1,33 @@
+package by.andd3dfx.string;
+
+/**
+ * <pre>
+ * <a href="https://leetcode.com/problems/is-subsequence/description/">Task description</a>
+ *
+ * Given two strings s and t, return true if s is a subsequence of t, or false otherwise.
+ * A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters
+ * without disturbing the relative positions of the remaining characters. (i.e., "ace" is a subsequence of "abcde" while "aec" is not).
+ *
+ * Example 1:
+ *   Input: s = "abc", t = "ahbgdc"
+ *   Output: true
+ *
+ * Example 2:
+ *   Input: s = "axc", t = "ahbgdc"
+ *   Output: false
+ * </pre>
+ */
+public class IsSubsequence {
+
+    public static boolean isSubsequence(String s, String t) {
+        var last = -1;
+        for (var ch : s.toCharArray()) {
+            var index = t.indexOf(ch, last + 1);
+            if (index == -1) {
+                return false;
+            }
+            last = index;
+        }
+        return true;
+    }
+}

src/test/java/by/andd3dfx/string/IsSubsequenceTest.java

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+package by.andd3dfx.string;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.Test;
+
+public class IsSubsequenceTest {
+
+    @Test
+    public void isSubsequence() {
+        assertThat(IsSubsequence.isSubsequence("abc", "ahbgdc")).isTrue();
+        assertThat(IsSubsequence.isSubsequence("axc", "ahbgdc")).isFalse();
+
+        assertThat(IsSubsequence.isSubsequence("abc", "aaccbb")).isFalse();
+        assertThat(IsSubsequence.isSubsequence("andrei", "rtaanghtdretyia")).isTrue();
+    }
+}