upload Lesson 14

Author: Mickey0521

14-BinarySearch_cckao.pdf

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+# you can write to stdout for debugging purposes, e.g.
+# print("this is a debug message")
+
+import math
+
+def solution(K, M, A):
+    # write your code in Python 3.6
+    
+    # try to find minMaxSum 
+    # we can try 'minMaxSum' by using binary search (fast)
+    # but, we need to know 
+    # min_possible_sum and max_possible_sum
+    # so, we can try mid_possible_sum (using binary search)
+    
+    # 1. find min_possible_sum and max_possible_sum
+    min_possible_sum = 0 
+    max_possible_sum = 0
+    for item in A:
+        min_possible_sum = max(min_possible_sum, item) # at least one element (large)
+        max_possible_sum += item # at most all elements (sum of all)
+    #print(min_possible_sum)
+    #print(max_possible_sum)
+    
+    # 3. check if mid_possible_sum is 'ok' or not (define the method)
+    def check_if_mid_sum_possible(K, M, A, mid_sum):
+        num_block_allowed = K
+        current_block_sum = 0 
+        for item in A:
+            current_block_sum += item
+            if current_block_sum > mid_sum: # need another block
+                num_block_allowed -= 1
+                current_block_sum = item # important (the item in next block)
+                if num_block_allowed ==0:
+                    return False
+        # all blocks can be smaller than (or equal to) mid_sum
+        return True
+    
+    # 2. binary search
+    result = max_possible_sum
+    
+    while min_possible_sum <= max_possible_sum:
+        mid_possible_sum = math.ceil( (min_possible_sum + max_possible_sum) / 2 )
+        # print(mid_possible_sum)
+        
+        # try smaller 
+        is_sum_possible = check_if_mid_sum_possible(K, M, A, mid_possible_sum)
+        # print(is_sum_possible)
+        if is_sum_possible == True:
+            result = mid_possible_sum
+            max_possible_sum = mid_possible_sum - 1
+        
+        # try bigger
+        else:
+            min_possible_sum = mid_possible_sum + 1
+    
+    return result
+