LeetCode-in-All

221. Maximal Square

Medium

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.

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: 4

Example 2:

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'.

Solution

func maximalSquare(matrix [][]byte) int {
	m := len(matrix)
	if m == 0 {
		return 0
	}
	n := len(matrix[0])
	if n == 0 {
		return 0
	}
	dp := make([][]int, m+1)
	for i := range dp {
		dp[i] = make([]int, n+1)
	}
	max := 0
	for i := 0; i < m; i++ {
		for j := 0; j < n; j++ {
			if matrix[i][j] == '1' {
				// 1 + minimum from cell above, cell to the left, cell diagonal upper-left
				next := 1 + min(dp[i][j], min(dp[i+1][j], dp[i][j+1]))
				// keep track of the maximum value seen
				if next > max {
					max = next
				}
				dp[i+1][j+1] = next
			}
		}
	}
	return max * max
}

func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}

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