A solution added for LC #85

src/main/java/org/sean/dynamicpro/MaxRectangle.java

@@ -0,0 +1,58 @@
+package org.sean.dynamicpro;
+
+import java.util.Stack;
+
+/***
+ * 85. Maximal Rectangle
+ */
+public class MaxRectangle {
+ private int[][] verticalSums;
+ private int maxArea = 0;
+
+ private void findMaxArea(int[] row) {
+ Stack<int[]> stack = new Stack<>();
+ for (int i = 0; i < row.length; i++) {
+ int len = row[i];
+ if (stack.isEmpty() || stack.peek()[1] < len) {
+ stack.push(new int[]{i, len});
+ } else {
+ // monotonic stack
+ int target = i;
+ while (!stack.isEmpty() && stack.peek()[1] >= len) {
+ int[] arr = stack.pop();
+ maxArea = Math.max(maxArea, arr[1] * (i - arr[0]));
+
+ // update the index for the new added item
+ target = arr[0];
+ }
+ stack.push(new int[]{target, len});
+ }
+ }
+ }
+
+ public int maximalRectangle(char[][] matrix) {
+ if (matrix == null || matrix.length == 0) {
+ return 0;
+ }
+
+ int rows = matrix.length;
+ int cols = matrix[0].length;
+
+ // extra row + column added for marking it as the end, all historical record will be evaluated.
+ verticalSums = new int[rows + 1][cols + 1];
+ for (int i = 0; i < rows; i++) {
+ for (int j = 0; j < cols; j++) {
+ if (matrix[i][j] == '0') {
+ verticalSums[i][j] = 0;
+ } else {
+ verticalSums[i][j] = i > 0 ? verticalSums[i - 1][j] + 1 : 1;
+ }
+ }
+ }
+ for (int i = 0; i < rows; i++) {
+ findMaxArea(verticalSums[i]);
+ }
+
+ return maxArea;
+ }
+}

src/test/java/org/sean/dynamicpro/MaxRectangleTest.java

@@ -0,0 +1,27 @@
+package org.sean.dynamicpro;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class MaxRectangleTest {
+
+ private MaxRectangle rect;
+
+ @Before
+ public void setUp() throws Exception {
+ rect = new MaxRectangle();
+ }
+
+ @Test
+ public void maximalRectangle() {
+ int res = rect.maximalRectangle(new char[][]{
+ {'1', '0', '1', '0', '0'},
+ {'1', '0', '1', '1', '1'},
+ {'1', '1', '1', '1', '1'},
+ {'1', '0', '0', '1', '0'}
+ });
+ assertEquals(6, res);
+ }
+}