题目：原题链接（中等）
标签：数组、动态规划
解法 | 时间复杂度 | 空间复杂度 | 执行用时 |
Ans 1 (Python) | O ( M × N ) | O ( M × N ) | 1224ms (71.14%) |
Ans 2 (Python) | |||
Ans 3 (Python) |
解法一：
class Solution:
def matrixBlockSum(self, mat: List[List[int]], K: int) -> List[List[int]]:
m, n = len(mat), len(mat[0])
# 计算前缀和
prefix = [[0] * (n + 1) for _ in range(m + 1)]
for i in range(1, m + 1):
for j in range(1, n + 1):
prefix[i][j] = prefix[i - 1][j] + prefix[i][j - 1] - prefix[i - 1][j - 1] + mat[i - 1][j - 1]
# 计算范围内的和
def count(x1, y1, x2, y2):
return prefix[x2][y2] - prefix[x1 - 1][y2] - prefix[x2][y1 - 1] + prefix[x1 - 1][y1 - 1]
ans = [[0] * n for _ in range(m)]
for i in range(m):
for j in range(n):
ans[i][j] += count(max(i - K, 0) + 1, max(j - K, 0) + 1, min(i + K, m - 1) + 1, min(j + K, n - 1) + 1)
return ans
