diff --git a/dsa-solutions/lc-solutions/0200-0299/221 - Maximal Square.md b/dsa-solutions/lc-solutions/0200-0299/221 - Maximal Square.md new file mode 100644 index 000000000..22a2cdfd0 --- /dev/null +++ b/dsa-solutions/lc-solutions/0200-0299/221 - Maximal Square.md @@ -0,0 +1,130 @@ +--- +id: maximal-square +title: Maximal Square +sidebar_label: 221 Maximal Square +tags: +- Dynamic Programming +- Java +- Matrix +- Array +description: "This document provides a solution where we find the largest square containing only 1's and return its area." +--- + +## Problem + +You are given an m x n binary $matrix$ filled with 0's and 1's, find the largest square containing only 1's and return its area. + +### Examples + +**Example 1:** + +![image](https://github.com/vivekvardhan2810/codeharborhub.github.io/assets/91594529/4816deda-e3ba-47d4-b6d8-b38dd4fe67e2) + +**Input:** matrix = [["1","0","1","0","0"],["1","0","1","1","1"],["1","1","1","1","1"],["1","0","0","1","0"]] + +**Output:** 4 + +**Example 2:** + +![image](https://github.com/vivekvardhan2810/codeharborhub.github.io/assets/91594529/43f9556f-bdde-4d5c-b8ab-a5807c51cb3c) + +**Input:** matrix = [["0","1"],["1","0"]] + +**Output:** 1 + +**Example 3:** + +**Input:** matrix = [["0"]] + +**Output:** 0 + +### Constraints + +- $m == matrix.length$ +- $n == matrix[i].length$ +- $1 <= m, n <= 300$ +- $matrix[i][j]$ is $0$ or $1$ + +--- +## Approach +There are four approaches discussed that helps to obtain the solution: + +1. **Dynamic Programming Table**: + - Use a 2D DP array **'dp'** where **'dp[i][j]'** represents the side length of the largest square whose bottom-right corner is at position **'(i, j)'**. + + - The value of **'dp[i][j]'** is determined by the values of **'dp[i-1][j]'**, **'dp[i][j-1]'**, and **'dp[i-1][j-1]'**. + +2. **Transition**: + + - If **'matrix[i][j]'** is $1$: + - If **'i'** or **'j'** is $0$ (first row or first column), **'dp[i][j]'** is $1$ because the largest square ending there can only be of $size1$. + + - Otherwise, **'dp[i][j]'** is the minimum of **'dp[i-1][j]'**, **'dp[i][j-1]'**, and **'dp[i-1][j-1]'** plus $1$. This is because we can form a larger square only if all three adjacent squares can also form squares of $1's$. + +3. **Max Side Length**: + + - Track the maximum side length of squares found during the iteration. + +4. **Result**: + + - The area of the largest square is the square of the maximum side length found. + +## Solution for Maximal Square + +This problem can be solved using dynamic programming. The problem requires to Utilize a DP table where each entry represents the side length of the largest square ending at that position. + +#### Code in Java + + ```java +class Solution { + public int maximalSquare(char[][] matrix) { + if (matrix == null || matrix.length == 0 || matrix[0].length == 0) { + return 0; + } + + int rows = matrix.length; + int cols = matrix[0].length; + int maxSide = 0; + + // Create a DP array to store the size of the largest square ending at each position + int[][] dp = new int[rows][cols]; + + // Fill the DP array + for (int i = 0; i < rows; i++) { + for (int j = 0; j < cols; j++) { + if (matrix[i][j] == '1') { + if (i == 0 || j == 0) { + // If we're at the first row or first column, the largest square ending here is just 1 + dp[i][j] = 1; + } else { + // Otherwise, calculate the size of the square based on the surrounding squares + dp[i][j] = Math.min(Math.min(dp[i-1][j], dp[i][j-1]), dp[i-1][j-1]) + 1; + } + // Update the maximum side length found + maxSide = Math.max(maxSide, dp[i][j]); + } + } + } + + // The area of the largest square is side length squared + return maxSide * maxSide; + } +} + +``` + +### Complexity Analysis + +#### Time Complexity: O($m$ x $n$) + +> **Reason**: The algorithm involves iterating through each cell of the matrix once, leading to a time complexity of $𝑂(𝑚 × 𝑛)$, where $𝑚$ is the number of rows and $𝑛$ is the number of columns. + +#### Space Complexity: O($m$ × $n$) + +> **Reason**: The space complexity is $𝑂(𝑚 × 𝑛)$ due to the additional DP array used. This could be optimized to $O(n)$ by reusing a single row of DP values, but in the given solution, we use a full 2D DP array. + +# References + +- **LeetCode Problem:** [Maximal Square](https://leetcode.com/problems/maximal-square/description/) +- **Solution Link:** [Maximal Square Solution on LeetCode](https://leetcode.com/problems/maximal-square/solutions/) +- **Authors LeetCode Profile:** [Vivek Vardhan](https://leetcode.com/u/vivekvardhan43862/)