1277. Count Square Submatrices with All Oness

Stanislav Gumeniuk included in Leetcode Leetcode-Problem

2020-05-21 210 words One minute

Contents

Problem solution 1277 “Count Square Submatrices with All Oness” from LeetCode.

Problem

Given a m * n matrix of ones and zeros, return how many square submatrices have all ones.

Constraints:

1 <= len(arr) <= 300
1 <= len(arr[0]) <= 300
0 <= arr[i][j] <= 1

example

Input: matrix = 
[
  [1,0,1],
  [1,1,0],
  [1,1,0]
]
Output: 7
Explanation: 
There are 6 squares of side 1.  
There is 1 square of side 2. 
Total number of squares = 6 + 1 = 7.

Input: matrix =
[
  [0,1,1,1],
  [1,1,1,1],
  [0,1,1,1]
]
Output: 15
Explanation: 
There are 10 squares of side 1.
There are 4 squares of side 2.
There is  1 square of side 3.
Total number of squares = 10 + 4 + 1 = 15.

Solution

DFS

func countSquares(matrix [][]int) int {
    sum:=0
    for i:=range matrix {
        for j:=range matrix[i] {
            sum+=helper(matrix, i, j, 0)
        }
    }
    return sum
}

func helper(m [][]int, i,j,l int) int {
    if i>=len(m) || j>=len(m[0] ) {
        return 0
    }
    if m[i][j] == 0 {
        return 0
    }
    sum := 0
   
    f := true
    for idx:=1; idx<=l;idx++ {
        f = f && i-idx>=0 && j-idx>=0 &&m[i-idx][j] == 1 &&m[i][j-idx] == 1
    }
    
    if f {
        sum++
        sum += helper(m,i+1,j+1,l+1)
    }
    
    return sum
}