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MaximalRectangleBinaryMatrix.java
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MaximalRectangleBinaryMatrix.java
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package Leetcode;
import java.util.ArrayDeque;
import java.util.Arrays;
import java.util.Deque;
/**
* @author kalpak
*
* Given a rows x cols binary matrix filled with 0's and 1's, find the largest rectangle containing only 1's and return its area.
*
* Example 1:
*
* Input: matrix = [["1","0","1","0","0"],["1","0","1","1","1"],["1","1","1","1","1"],["1","0","0","1","0"]]
* Output: 6
* Explanation: The maximal rectangle is shown in the above picture.
*
* Example 2:
* Input: matrix = []
* Output: 0
*
* Example 3:
* Input: matrix = [["0"]]
* Output: 0
*
* Example 4:
* Input: matrix = [["1"]]
* Output: 1
*
* Example 5:
* Input: matrix = [["0","0"]]
* Output: 0
*
*
* Constraints:
*
* rows == matrix.length
* cols == matrix.length
* 0 <= row, cols <= 200
* matrix[i][j] is '0' or '1'.
*/
public class MaximalRectangleBinaryMatrix {
public static int maximalRectangle(char[][] matrix) {
if(matrix.length == 0)
return 0;
int result = 0;
int[] heights = new int[matrix[0].length];
for(int i = 0; i < matrix.length; i++) {
for(int j = 0; j < matrix[0].length; j++) {
heights[j] = matrix[i][j] == '1' ? heights[j] + 1 : 0;
}
result = Math.max(result, largestRectangleArea(heights));
}
return result;
}
private static int largestRectangleArea(int[] heights) {
int[] firstSmallerToLeft = new int[heights.length];
int[] firstSmallerToRight = new int[heights.length];
Deque<Integer> stack = new ArrayDeque<>();
int result = 0;
Arrays.fill(firstSmallerToLeft, -1);
Arrays.fill(firstSmallerToRight, heights.length);
for (int i = 0; i < heights.length; i++) {
while (!stack.isEmpty() && (heights[stack.peek()] >= heights[i])) {
firstSmallerToRight[stack.poll()] = i;
}
if(!stack.isEmpty())
firstSmallerToLeft[i] = stack.peek();
stack.push(i);
}
for (int i = 0; i < heights.length; i++) {
result = Math.max(result, heights[i] * (firstSmallerToRight[i] - firstSmallerToLeft[i] - 1));
}
return result;
}
public static void main(String[] args) {
char[][] arr = new char[][]{{'1','0','1','0','0'},{'1','0','1','1','1'},{'1','1','1','1','1'},{'1','0','0','1','0'}};
System.out.println(maximalRectangle(arr));
}
}