1 class Solution: 2 def matrixBlockSum(self, mat: 'List[List[int]]', K: int) -> 'List[List[int]]': 3 r,c = len(mat),len(mat[0]) 4 prefixsum = [[0 for _ in range(c)]for _ in range(r)] 5 for i in range(r): 6 prefixsum[i][0] = mat[i][0] 7 for j in range(1,c): 8 prefixsum[i][j] = mat[i][j] + prefixsum[i][j-1] 9 for j in range(c): 10 for i in range(1,r): 11 prefixsum[i][j] = prefixsum[i-1][j] + prefixsum[i][j] 12 #print(prefixsum) 13 res = [[0 for _ in range(c)]for _ in range(r)] 14 for i in range(r): 15 for j in range(c): 16 r_low,r_high = max(i - K,0),min(i + K,r-1) 17 c_low,c_high = max(j - K,0),min(j + K,c-1) 18 #print(r_low,c_low,r_high,c_high) 19 20 if r_low >= 1 and c_low >= 1: 21 res[i][j] = prefixsum[r_high][c_high] - prefixsum[r_low-1][c_high] - prefixsum[r_high][c_low-1] + prefixsum[r_low-1][c_low-1] 22 elif r_low >= 1 and c_low == 0: 23 res[i][j] = prefixsum[r_high][c_high] - prefixsum[r_low-1][c_high] 24 elif r_low == 0 and c_low >= 1: 25 res[i][j] = prefixsum[r_high][c_high] - prefixsum[r_high][c_low-1] 26 else: 27 res[i][j] = prefixsum[r_high][c_high] 28 return res
算法思路：二维矩阵求和。
先计算前序和，然后计算矩形子区域的和。共分4种情况讨论。
