Fix the program

Author: Xuefeng-Zhu

misc/max_area_histogram.py

@@ -10,7 +10,7 @@
 
 """
 
-# hist represented as ith bar has height h(i) 
+# hist represented as ith bar has height h(i)
 histogram = [6, 4, 2, 1, 3, 4, 5, 2, 6]
 
 """
@@ -21,26 +21,29 @@
 4. compute max area
 """
 
-def get_L(hist):
-    L = [0]*len(hist)
-    for i in range(1, len(hist)):
-        if hist[i] > hist[i-1]:
-            L[i] = i
+
+def find_Li(hist, i):
+    left_edge = 0
+    for j in range(i-1, -1, -1):
+        if hist[j] >= hist[i]:
+            left_edge += 1
         else:
-            L[i] = L[i-1]
-    return L
+            return left_edge
+
+    return left_edge
 
-print get_L(histogram)
 
 def find_Ri(hist, i):
     right_edge = 0
-    for j in range(i+1, len(hist)):
+    for j in range(i + 1, len(hist)):
         if hist[j] >= hist[i]:
             right_edge += 1
         else:
             return right_edge
+
     return right_edge
 
+
 def get_area(hist, i):
     return hist[i] * (find_Li(hist, i) + find_Ri(hist, i) + 1)
 
@@ -53,6 +56,7 @@ def get_max_area(hist):
             max_area = area
     return max_area
 
+
 def max_rectangle_area(histogram):
     """Find the area of the largest rectangle that fits entirely under
     the histogram.
@@ -61,21 +65,21 @@ def max_rectangle_area(histogram):
     stack = []
     top = lambda: stack[-1]
     max_area = 0
-    pos = 0 # current position in the histogram
+    pos = 0  # current position in the histogram
     for pos, height in enumerate(histogram):
-        start = pos # position where rectangle starts
+        start = pos  # position where rectangle starts
         while True:
-            if not stack or height > top().height:
-                stack.append(Info(start, height)) # push
-            elif stack and height < top().height:
-                max_area = max(max_area, top().height*(pos-top().start))
+            if not stack or height > top()[1]:
+                stack.append((start, height))  # push
+            elif stack and height < top()[1]:
+                max_area = max(max_area, top()[1] * (pos - top()[0]))
                 start, _ = stack.pop()
                 continue
-            break # height == top().height goes here
+            break  # height == top().height goes here
 
     pos += 1
     for start, height in stack:
-        max_area = max(max_area, height*(pos-start))
+        max_area = max(max_area, height * (pos - start))
 
     return max_area