MediumNo. 0533LeetCode Premium
Lonely Pixel II — LeetCode 533 Python Solution
- Pattern
- Matrix and Grid
- Topics
- Array, Hash Table, Matrix
- Reading time
- 3 min
- Source
- leetcode.com
The problem
Given an m x n picture consisting of black 'B' and white 'W' pixels and an integer target, return the number of black lonely pixels. A black lonely pixel is a character 'B' that located at a specific position (r, c) where: Row r and column c both contain exactly target black pixels.
Example
- Input
- picture = [["W","B","W","B","B","W"],["W","B","W","B","B","W"],["W","B","W","B","B","W"],["W","W","B","W","B","W"]], target = 3
- Output
- 6
- Explanation
- All the green 'B' are the black pixels we need (all 'B's at column 1 and 3).
Python solution
class Solution:
def findBlackPixel(self, picture: List[List[str]], target: int) -> int:
rows = [0] * len(picture)
g = defaultdict(list)
for i, row in enumerate(picture):
for j, x in enumerate(row):
if x == "B":
rows[i] += 1
g[j].append(i)
ans = 0
for j in g:
i1 = g[j][0]
if rows[i1] != target:
continue
if len(g[j]) == rows[i1] and all(picture[i2] == picture[i1] for i2 in g[j]):
ans += target
return ansComplexity
- Time
- O(m × n2)
- Space · auxiliary
- O(m × n)where m and n are the number of rows and columns in the matrix respectively
Pattern: Matrix and Grid
Treat a 2-D grid as a graph whose neighbours are the four adjacent cells. LeetCode 533. Lonely Pixel II is filed here because LeetCode tags it Matrix, which is the vocabulary this hub collects.
The matrix and grid guide has the Python template for the pattern and the 216 LeetCode problems that use it.
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Frequently asked questions
- How hard is LeetCode 533. Lonely Pixel II?
LeetCode 533. Lonely Pixel II is rated Medium on LeetCode.
- What is the time complexity of LeetCode 533. Lonely Pixel II?
The Python solution on this page runs in O(m × n2).
- What is the space complexity of LeetCode 533. Lonely Pixel II?
The Python solution on this page uses O(m × n), where m and n are the number of rows and columns in the matrix respectively auxiliary space.
- What topics does LeetCode 533. Lonely Pixel II cover?
LeetCode 533. Lonely Pixel II is tagged Array, Hash Table and Matrix on LeetCode.
- Is LeetCode 533. Lonely Pixel II a premium problem?
Yes. LeetCode 533. Lonely Pixel II is a LeetCode Premium problem, so the full statement and test cases require a paid LeetCode subscription.