跳到主要内容

常见错误

Mistake 1: Confusing Row and Column Bounds​

' Wrong — dimensions reversed
DECLARE arr : ARRAY[1:5, 1:10] OF INTEGER  ' Intended: 10 rows, 5 cols

Fix: First dimension = rows, second = columns. Always match the problem description.

Mistake 2: Off-by-One in Nested Loops​

' Wrong — loop starts at 0 but array is 1-indexed
FOR i ← 0 TO 9

Fix: Use 1 TO n, where n is the upper bound declared in the array.

Mistake 3: Sorting Only the Column Instead of Full Rows​

' Wrong — only swaps values in one column
IF arr[j][col] > arr[j+1][col] THEN
  temp ← arr[j][col]
  arr[j][col] ← arr[j+1][col]
  arr[j+1][col] ← temp

Fix: Store and swap entire rows (or store row as key and shift), not just one column's value.

Mistake 4: Binary Tree — Forgetting to Set Child Pointers to -1​

' Wrong — new node's LeftPointer and RightPointer left uninitialised
Tree[nextFree][DataCol] ← newData
' No pointer initialisation!

Fix: Always set both pointers to -1 for any new node.

Mistake 5: Binary Tree — Comparing Wrong Column​

' Wrong — comparing against LeftPointer column instead of Data
IF newData < Tree[current][LeftCol] THEN

Fix: Compare newData against Tree[current][DataCol], not against a pointer.

Mistake 6: Binary Tree — Updating Wrong Parent's Pointer​

' Wrong — modifies current node's pointer instead of parent's
current ← Tree[current][LeftCol]
IF Tree[current][LeftCol] = -1 THEN
  Tree[current][LeftCol] ← freeRow  ' This is the child, not parent!

Fix: Before moving current, check if the next node to visit would be -1. If so, update the current node's pointer before moving.

Mistake 7: Using 1D Array Instead of 2D​

DECLARE arr : ARRAY[1:50] OF INTEGER  ' Wrong for question needing 2D

Fix: If the question says "store rows and columns", you must use ARRAY[1:r, 1:c].

Mistake 8: Incorrect Binary Tree Traversal Order​

' Wrong order for in-order traversal
OUTPUT Tree[index][DataCol]
CALL InOrder(Tree, Tree[index][LeftCol])
CALL InOrder(Tree, Tree[index][RightCol])

Fix:

  • In-order: Left → Data → Right
  • Pre-order: Data → Left → Right
  • Post-order: Left → Right → Data

Mistake 9: Array Declaration Inside Loop​

FOR i ← 1 TO 10
  DECLARE arr : ARRAY[1:5, 1:3] OF INTEGER  ' Wrong — redeclares each iteration

Fix: Declare once before any loop.

Mistake 10: Pointer vs Index Confusion in Binary Tree​

Root pointer indicates which row is the tree root, not the index of a column. The array indices are the "nodes". A pointer value of -1 means "no node", not row 0.

' Correct: root variable stores a row index
IF root = -1 THEN
  root ← freeRow