考前速记

Quick Reference

Task	Code
Declare 1D array (size 10)	`Arr = [0] * 10`
Declare 2D array (3 × 4)	`Arr = [[0] * 4 for i in range(3)]`
Traverse 1D	`for i in range(len(Arr)):`
Traverse 2D	`for r in range(R): for c in range(C):`
Read input to array	`Arr[i] = int(input(...))`
Sum all elements	`Total = Total + Arr[i]`
Find max	`if Arr[i] > Max: Max = Arr[i]`
Search	`if Arr[i] == SearchValue:`
Global declaration	`global Arr` before assignment

Fill-and-process template

def main():
    global Arr
    Arr = [0] * 10
    for i in range(10):
        Arr[i] = int(input())
    # process Arr here

Find average

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

Red Flag	What to Check
`global` used?	If declaring array inside a function, yes
`range(1, N+1)`	Off-by-one — should be `range(N)`
`Arr = []` then `Arr[i] = x`	Must use `append()` or pre-allocate
`[0] * N` for 2D	Shallow copy bug — use comprehension
`input()` without `int()`	String stored instead of number
Loop bounds wrong way round	Rows first, columns second in 2D
`if Arr[i] = x`	Should be `==` not `=`
Array name spelling	Must match exactly what question gives

备注

M1 = method / structure (loop, function, file open)

A1 = accuracy (correct variable, correct indexing)

B1 = bonus / alternative (type conversion, edge case)