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src/main/java/org/gd/leetcode/p0084/Solution.java

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+package org.gd.leetcode.p0084;
+
+import org.gd.leetcode.common.LeetCode;
+
+/**
+ * https://leetcode.com/problems/largest-rectangle-in-histogram/
+ */
+@LeetCode(
+        name = "Largest Rectangle in Histogram",
+        difficulty = LeetCode.Level.HARD,
+        state = LeetCode.State.TODO,
+        tags = {
+                LeetCode.Tags.ARRAY,
+                LeetCode.Tags.STACK
+        }
+)
+class Solution {
+
+    public int largestRectangleArea(int[] heights) {
+
+        if (heights == null || heights.length == 0)
+            return 0;
+
+        if (heights.length == 1)
+            return heights[0];
+
+        int max = 0;
+        for (int i = 0; i < heights.length; i++) {
+
+            max = Math.max(max, heights[i]);
+            int lowestHeight = heights[i];
+
+            for (int j = i + 1; j < heights.length; j++) {
+
+                int width = j - i + 1;
+                lowestHeight = Math.min(lowestHeight, heights[j]);
+                max = Math.max(max, width * lowestHeight);
+
+            }
+        }
+        return max;
+    }
+}

src/test/java/org/gd/leetcode/p0084/SolutionTest.java

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+package org.gd.leetcode.p0084;
+
+import org.junit.jupiter.api.*;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+import java.util.stream.Stream;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+@DisplayName("LeetCode #84: Largest Rectangle in Histogram")
+class SolutionTest {
+
+    private static Stream<Arguments> args() {
+        return Stream.of(
+                Arguments.of(new int[]{2, 1, 5, 6, 2, 3}, 10)
+        );
+    }
+
+    @ParameterizedTest
+    @MethodSource("args")
+    void largestRectangleArea(int[] area, int expected) {
+        assertEquals(expected, new Solution().largestRectangleArea(area));
+    }
+}