解题方法

Method 1: Declaring Global Arrays in Python

When an array is declared inside a function (e.g. main()) and needs to be accessible from other functions, global is required.

Standard Method

def main():
    global MyArray
    MyArray = [0] * 10
    ...

Key rule: Declare global before assigning the array. Without global, Python creates a local variable.

Alternative — Return value

Instead of global, declare in main() and pass as a parameter:

def main():
    MyArray = [0] * 10
    process(MyArray)

def process(Arr):
    # Arr receives reference to MyArray
    ...

When to use each:

• Use global when the array must be accessed by many functions without parameter passing
• Use parameter passing when you want to control data flow and avoid side effects

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Method 2: Reading Data from User into Array

Standard pattern for filling an array with user input:

Standard Method

def main():
    global Scores
    Scores = [0] * 10
    for i in range(10):
        Scores[i] = int(input("Enter score: "))

Variations:

Scenario	Pattern
String data	Array[i] = input(...) (no int())
Unknown size	Use while loop with sentinel, append()
File input	Array[i] = int(File.readline())
With validation	Loop until valid, then store

Example — Reading until sentinel ($-1$):

def main():
    global Values
    Values = []
    Value = int(input("Enter value (-1 to stop): "))
    while Value != -1:
        Values.append(Value)
        Value = int(input("Enter value (-1 to stop): "))

Warning: When using append(), do NOT pre-allocate with [0] * N.

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Method 3: Processing Array Elements with Loops

Standard Method — Sum and Average

Total = 0
for i in range(len(Array)):
    Total = Total + Array[i]
Average = Total / len(Array)

Standard Method — Find Maximum

Max = Array[0]
for i in range(1, len(Array)):
    if Array[i] > Max:
        Max = Array[i]

Standard Method — Linear Search

Found = False
Index = 0
while Index < len(Array) and not Found:
    if Array[Index] == SearchValue:
        Found = True
    else:
        Index = Index + 1
if Found:
    print("Found at position", Index)
else:
    print("Not found")

Standard Method — 2D Array Traversal (row-major)

for r in range(ROWS):
    for c in range(COLS):
        # process Array[r][c]