SWUST Parsons practice questions: P118. Array catching rain

describe

Given an integer arrayarr**, all the The values are all non-negative. Think of this array as a column height map, and calculate how much rain the columns arranged in this way can catch after it rains. (The height of the area outside the array is regarded as0)**

Number of units: Number of units of length** 0≤n≤2×10^5^，Number of pairs per unit is full 0<val≤10^9^ 0≤val≤10^9^ **，guaranteed return result complete

Sample

enter

3,1,2,5,2,4

output

Code:

height = [int(x) for x in input().split(',')]
n = len(height)
left, right = 0, n - 1
left_max, right_max = height[0], height[n - 1]
summ = 0
while left <= right:
    left_max = max(left_max, height[left])
    right_max = max(right_max, height[right])
    if left_max < right_max:
        summ += left_max - height[left]
        left += 1
    else:
        summ += right_max - height[right]
        right -= 1
print(summ)

Code analysis:

height = input().split(',')
height = [int(x) for x in height]
These two lines of code take user input and convert the input string into a list of strings using comma delimiters.

Then, use a list comprehension to convert each element in the list of strings to an integer, and store the result in the height list.
n = len(height)
left, right = 0, n - 1
left_max, right_max = height[0], height[n - 1]
summ = 0
This part of the code initializes the variablen, which represents the length of the input listheight.

In addition, the left pointer (left) and the right pointer (right) are defined and initialized to the first and last elements of the list index of.

left_max and right_max represent the maximum heights on the left and right sides respectively, which are set to the heights of the first and last elements of the list respectively by default.

Finally, the variablesumm is used to accumulate the results and is initialized to 0.
while left <= right:
    left_max = max(left_max, height[left])
    right_max = max(right_max, height[right])
    
    if left_max < right_max:
        summ += left_max - height[left]
        left += 1
    else:
        summ += right_max - height[right]
        right -= 1
This part is the main calculation logic, using the double pointer method to traverse the elements in the list.

When the left pointer is less than or equal to the right pointer, the loop is executed.

In each loop, by comparing the heights of the corresponding positions of the left and right pointers, the maximum height on the left (left_max) and the maximum height on the right (right_max).

If the maximum height on the left is less than the maximum height on the right, calculate and accumulate the rainwater amount:left_max - height[left], and move the left pointer one position to the right.

Otherwise, calculate and accumulate the amount of rainwater:right_max - height[right], and move the right pointer one position to the left.
print(summ)
Finally, print the accumulated rain volume.