Create maximum-non-negative-product-in-a-matrix.py

Author: kamyu104

Python/maximum-non-negative-product-in-a-matrix.py

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+# Time:  O(m * n)
+# Space: O(n)
+
+# dp with rolling window
+class Solution(object):
+    def maxProductPath(self, grid):
+        """
+        :type grid: List[List[int]]
+        :rtype: int
+        """
+        MOD = 10**9+7
+        max_dp = [[0]*len(grid[0]) for _ in xrange(2)]
+        min_dp = [[0]*len(grid[0]) for _ in xrange(2)]
+        for i in xrange(len(grid)):
+            for j in xrange(len(grid[i])):
+                if i == 0 and j == 0:
+                    max_dp[i%2][j] = min_dp[i%2][j] = grid[i][j]
+                    continue
+                curr_max = max(max_dp[(i-1)%2][j] if i > 0 else max_dp[i%2][j-1],
+                               max_dp[i%2][j-1] if j > 0 else max_dp[(i-1)%2][j])
+                curr_min = min(min_dp[(i-1)%2][j] if i > 0 else min_dp[i%2][j-1],
+                               min_dp[i%2][j-1] if j > 0 else min_dp[(i-1)%2][j])
+                if grid[i][j] < 0:
+                    curr_max, curr_min = curr_min, curr_max
+                max_dp[i%2][j] = curr_max*grid[i][j]
+                min_dp[i%2][j] = curr_min*grid[i][j]
+        return max_dp[(len(grid)-1)%2][-1]%MOD if max_dp[(len(grid)-1)%2][-1] >= 0 else -1