solves maximal square in java

Author: anishLearnsToCode

README.md

@@ -178,7 +178,7 @@
 | 217  | [Contains Duplicate](https://leetcode.com/problems/contains-duplicate)                                                                                    |                                 [![Java](assets/java.png)](src/ContainsDuplicate.java) [![Python](assets/python.png)](python/contains_duplicate.py)                                  |                                                                                                                                   |
 | 219  | [Contains Duplicate II](https://leetcode.com/problems/contains-duplicate-ii)                                                                              |                               [![Java](assets/java.png)](src/ContainsDuplicateII.java) [![Python](assets/python.png)](python/contains_duplicate_ii.py)                               |                                                                                                                                   |
 | 220  | [Contains Duplicate III](https://leetcode.com/problems/contains-duplicate-iii)                                                                            |                                                              [![Java](assets/java.png)](src/ContainsDuplicateIII.java)                                                               |                                                                                                                                   |
-| 221  | [Maximal Square](https://leetcode.com/problems/maximal-square)                                                                                            |                                                                                                                                                                                      |                                                                                                                                   |
+| 221  | [Maximal Square](https://leetcode.com/problems/maximal-square)                                                                                            |                                                                  [![Java](assets/java.png)](src/MaximalSquare.java)                                                                  |                                                                                                                                   |
 | 222  | [Count Complete Tree Nodes](https://leetcode.com/problems/count-complete-tree-nodes)                                                                      |                                                             [![Java](assets/java.png)](src/CountCompleteTreeNodes.java)                                                              |                                                                                                                                   |
 | 223  | [Rectangle Area](https://leetcode.com/problems/rectangle-area)                                                                                            |                                                                                                                                                                                      |                                                                                                                                   |
 | 225  | [Implement Stack using Queues](https://leetcode.com/problems/implement-stack-using-queues)                                                                |                                 [![Java](assets/java.png)](src/MyStack.java) [![Python](assets/python.png)](python/implement_stack_using_queues.py)                                  |                                                                                                                                   |

src/MaximalSquare.java

@@ -1,64 +1,32 @@
 // https://leetcode.com/problems/maximal-square
 // T: O(m * n)
-// S: O(m * n)
+// S: O(n)
 
 public class MaximalSquare {
     public int maximalSquare(char[][] matrix) {
-        final int rows = matrix.length, columns = matrix[0].length;
-        final int[][] dp = new int[rows][columns];
-
-        assignFirstRowInDPMatrix(dp, matrix);
-        assignFirstColumnInDPMatrix(dp, matrix);
-
-        int maxSideLen = contains1(dp) ? 1 : 0;
-
-        for (int row = 1 ; row < rows ; row++) {
-            for (int column = 1 ; column < columns ; column++) {
-                if (isOne(matrix[row][column])) {
-                    dp[row][column] = min(dp[row - 1][column], dp[row][column - 1], dp[row - 1][column - 1]) + 1;
-                } else dp[row][column] = 0;
-                maxSideLen = Math.max(maxSideLen, dp[row][column]);
+        final int columns = matrix[0].length;
+        final int[] dp = new int[columns + 1];
+        int maxSideLength = 0, prev = 0, temp;
+
+        for (char[] row : matrix) {
+            for (int column = 0; column < columns; column++) {
+                temp = dp[column + 1];
+                if (isOne(row[column])) {
+                    dp[column + 1] = min(dp[column + 1], dp[column], prev) + 1;
+                } else dp[column + 1] = 0;
+                maxSideLength = Math.max(maxSideLength, dp[column + 1]);
+                prev = temp;
             }
         }
 
-        return maxSideLen * maxSideLen;
-    }
-
-    private boolean contains1(int[][] dp) {
-        return contains1InFirstRow(dp) || contains1InFirstColumn(dp);
-    }
-
-    private boolean contains1InFirstRow(int[][] dp) {
-        for (int element : dp[0]) {
-            if (element == 1) return true;
-        }
-        return false;
-    }
-
-    private boolean contains1InFirstColumn(int[][] dp) {
-        for (int[] row : dp) {
-            if (row[0] == 1) return true;
-        }
-        return false;
-    }
-
-    private boolean isOne(char character) {
-        return character == '1';
+        return maxSideLength * maxSideLength;
     }
 
     private int min(int a, int b, int c) {
         return Math.min(a, Math.min(b, c));
     }
 
-    private void assignFirstRowInDPMatrix(int[][] dp, char[][] matrix) {
-        for (int column = 0 ; column < matrix[0].length ; column++) {
-            dp[0][column] = matrix[0][column] - '0';
-        }
-    }
-
-    private void assignFirstColumnInDPMatrix(int[][] dp, char[][] matrix) {
-        for (int row = 0 ; row < matrix.length ; row++) {
-            dp[row][0] = matrix[row][0] - '0';
-        }
+    private boolean isOne(char c) {
+        return c == '1';
     }
 }