Create 10. Trapping Rain Water II.py

08_Heap/10. Trapping Rain Water II.py

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+# https://leetcode.com/problems/trapping-rain-water-ii/
+# https://youtu.be/QvQiQcLCQ4Y
+
+import heapq
+class Solution:
+    def trapRainWater(self, heightMap):
+        minHeap = []
+        ROW, COL = len(heightMap), len(heightMap[0])
+        visited = [[False]*COL for _ in range(ROW)]
+
+        for i in range(ROW):
+            for j in range(COL):
+                if i in (0, ROW-1) or j in (0, COL-1):
+                    heapq.heappush(minHeap, (heightMap[i][j], i, j))
+                    visited[i][j] = True
+
+        res = 0
+        minBdH = 0  # Minimum Boundary Height
+        while minHeap:
+            h, i, j = heapq.heappop(minHeap)
+            minBdH = max(minBdH, h)
+            for dx, dy in ((1,0),(-1,0),(0,1),(0,-1)):
+                r, c = i+dx, j+dy
+                if 0<=r<ROW and 0<=c<COL and not visited[r][c]:
+                    visited[r][c] = True
+                    heapq.heappush(minHeap, (heightMap[r][c], r, c))
+                    if heightMap[r][c] < minBdH:
+                        res += minBdH - heightMap[r][c]
+
+        return res
+
+
+
+# Time: O(m*n * log(m*n))
+# Space: O(m*n)