How hard is LeetCode 1504. Count Submatrices With All Ones?

LeetCode 1504. Count Submatrices With All Ones is rated Medium on LeetCode.

What is the time complexity of LeetCode 1504. Count Submatrices With All Ones?

The Python solution on this page runs in O(m^2 \times n).

What is the space complexity of LeetCode 1504. Count Submatrices With All Ones?

The Python solution on this page uses O(m \times n) auxiliary space.

What topics does LeetCode 1504. Count Submatrices With All Ones cover?

LeetCode 1504. Count Submatrices With All Ones is tagged Stack, Array, Dynamic Programming, Matrix and Monotonic Stack on LeetCode.

Count Submatrices With All Ones — LeetCode 1504 Python Solution

MediumStackArrayDynamic ProgrammingMatrixMonotonic Stack

Problem: #1504
Pattern: Stack
Reading time: 3 min
Source: leetcode.com

The problem

Given an m x n binary matrix mat, return the number of submatrices that have all ones.

Example

Input: mat = [[1,0,1],[1,1,0],[1,1,0]]
Output: 13
Explanation: There are 6 rectangles of side 1x1.

Python solution

Python

class Solution:
    def numSubmat(self, mat: List[List[int]]) -> int:
        m, n = len(mat), len(mat[0])
        g = [[0] * n for _ in range(m)]
        for i in range(m):
            for j in range(n):
                if mat[i][j]:
                    g[i][j] = 1 if j == 0 else 1 + g[i][j - 1]
        ans = 0
        for i in range(m):
            for j in range(n):
                col = inf
                for k in range(i, -1, -1):
                    col = min(col, g[k][j])
                    ans += col
        return ans

Complexity

Measure	Complexity
Time	O(m^2 \times n)
Space	O(m \times n) auxiliary

Pattern: Stack

When the most recent unresolved thing is the one that matters, use a stack. LeetCode 1504. Count Submatrices With All Ones is filed here because LeetCode tags it Stack, which is the vocabulary this hub collects.

The stack guide has the Python template for the pattern and the 194 LeetCode problems that use it.

Frequently asked questions

How hard is LeetCode 1504. Count Submatrices With All Ones?: LeetCode 1504. Count Submatrices With All Ones is rated Medium on LeetCode.
What is the time complexity of LeetCode 1504. Count Submatrices With All Ones?: The Python solution on this page runs in O(m^2 \times n).
What is the space complexity of LeetCode 1504. Count Submatrices With All Ones?: The Python solution on this page uses O(m \times n) auxiliary space.
What topics does LeetCode 1504. Count Submatrices With All Ones cover?: LeetCode 1504. Count Submatrices With All Ones is tagged Stack, Array, Dynamic Programming, Matrix and Monotonic Stack on LeetCode.