MAANG - top

Author: Subham1999

.idea/workspace.xml

@@ -0,0 +1,66 @@
+package com.thealgorithm.stacks;
+
+import java.util.Arrays;
+import java.util.Stack;
+
+/**
+ * @author: Subham Santra
+ */
+public class LargestSubMatrixWithRearrangements {
+  public int largestSubmatrix(int[][] matrix) {
+    int m = matrix.length;
+    int n = matrix[0].length;
+    int[][] prefixSum = new int[m][n];
+
+    System.arraycopy(matrix[0], 0, prefixSum[0], 0, n);
+
+    for (int i = 1; i < m; ++i) {
+      for (int j = 0; j < n; ++j) {
+        prefixSum[i][j] = matrix[i][j] == 0 ? 0 : prefixSum[i - 1][j] + matrix[i][j];
+      }
+    }
+
+    int result = 0;
+
+    for (int i = 0; i < m; ++i) { // O(R)
+      // O(ClogC) + O(C) = O(ClogC)
+      Arrays.sort(prefixSum[i]); // O(ClogC)
+      result = Math.max(result, largestHistogram(prefixSum[i])); // O(C)
+    }
+
+    // Overall TC : O(RClogC) -> O(mn(log n))
+    return result;
+  }
+
+  private int largestHistogram(int[] arr) {
+    Stack<int[]> stack = new Stack<>();
+    int[] temp = new int[arr.length];
+    for (int i = 0; i < arr.length; ++i) {
+      int backIndex = i;
+      while (!stack.isEmpty() && (stack.peek()[0] > arr[i])) {
+        backIndex = stack.pop()[1];
+      }
+      temp[i] = arr[i] * (backIndex - i + 1);
+      stack.push(new int[] {arr[i], backIndex, i});
+    }
+    while (!stack.isEmpty()) {
+      temp[stack.peek()[2]] = stack.peek()[0] * (arr.length - stack.peek()[2]);
+      stack.pop();
+    }
+    return Arrays.stream(temp).max().orElse(0);
+  }
+
+  public static void main(String[] args) {
+    System.out.println(
+        new LargestSubMatrixWithRearrangements()
+            .largestSubmatrix(new int[][] {{1, 1, 0}, {1, 0, 1}}));
+
+    System.out.println(
+        new LargestSubMatrixWithRearrangements()
+            .largestSubmatrix(new int[][] {{0, 0, 1}, {1, 1, 1}, {1, 0, 1}}));
+
+    System.out.println(
+        new LargestSubMatrixWithRearrangements()
+            .largestSubmatrix(new int[][] {{1, 0, 1, 1, 0, 1}}));
+  }
+}