Create matrix-block-sum.py

Author: kamyu104

Python/matrix-block-sum.py

@@ -0,0 +1,21 @@
+# Time:  O(m * n)
+# Space: O(m * n)
+
+class Solution(object):
+    def matrixBlockSum(self, mat, K):
+        """
+        :type mat: List[List[int]]
+        :type K: int
+        :rtype: List[List[int]]
+        """
+        m, n = len(mat), len(mat[0])
+        accu = [[0 for _ in xrange(n+1)] for _ in xrange(m+1)]
+        for i in xrange(m):
+            for j in xrange(n):
+                accu[i+1][j+1] = accu[i+1][j]+accu[i][j+1]-accu[i][j]+mat[i][j]
+        result = [[0 for _ in xrange(n)] for _ in xrange(m)]        
+        for i in xrange(m):
+            for j in xrange(n):
+                r1, c1, r2, c2 = max(i-K, 0), max(j-K, 0), min(i+K+1, m), min(j+K+1, n)
+                result[i][j] = accu[r2][c2]-accu[r1][c2]-accu[r2][c1]+accu[r1][c1]
+        return result