Implement CountItemsMatchingARule1773 with complexity analysis and tests

src/main/java/com/leetcode/easy/CountItemsMatchingARule1773.java

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+// Tags: Array, String
+package com.leetcode.easy;
+
+import java.util.List;
+
+public class CountItemsMatchingARule1773 {
+    /**
+     * Let n = items.size().
+     * Time complexity: O(n)
+     * Breakdown:
+     * - Single for loop: Iterates through all items - O(n)
+     * - String comparison: O(1) per comparison (comparing with fixed ruleKey and ruleValue)
+     * Overall: O(n)
+     * <p>
+     * Space complexity: O(1)
+     * - Only uses a single integer variable 'res' - O(1)
+     */
+    public int countMatches(List<List<String>> items, String ruleKey, String ruleValue) {
+        int res = 0;
+        for (List<String> item : items) {
+            if (ruleKey.equals("type") && item.get(0).equals(ruleValue)) {
+                res++;
+            } else if (ruleKey.equals("color") && item.get(1).equals(ruleValue)) {
+                res++;
+            } else if (ruleKey.equals("name") && item.get(2).equals(ruleValue)) {
+                res++;
+            }
+        }
+        return res;
+    }
+}

src/test/java/com/leetcode/easy/CountItemsMatchingARule1773Test.java

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+package com.leetcode.easy;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class CountItemsMatchingARule1773Test {
+    private CountItemsMatchingARule1773 solution;
+
+    @BeforeEach
+    void setUp() {
+        solution = new CountItemsMatchingARule1773();
+    }
+
+    @Test
+    void testCountMatches_Example1() {
+        var items = List.of(
+                List.of("phone", "blue", "pixel"),
+                List.of("computer", "silver", "lenovo"),
+                List.of("phone", "gold", "iphone")
+        );
+        String ruleKey = "color";
+        String ruleValue = "silver";
+        int expected = 1;
+        int result = solution.countMatches(items, ruleKey, ruleValue);
+        assertEquals(expected, result);
+    }
+
+    @Test
+    void testCountMatches_Example2() {
+        var items = List.of(
+                List.of("phone", "blue", "pixel"),
+                List.of("computer", "silver", "lenovo"),
+                List.of("phone", "gold", "iphone")
+        );
+        String ruleKey = "type";
+        String ruleValue = "phone";
+        int expected = 2;
+        int result = solution.countMatches(items, ruleKey, ruleValue);
+        assertEquals(expected, result);
+    }
+}