#K89287. Validate and Correct Stack Operations
Validate and Correct Stack Operations
Validate and Correct Stack Operations
You are given a sequence of operations representing a stack manipulation. The operations include push x
, pop
, and inc k x
. The inc
operation increases each of the bottom k
elements of the stack by x
. If an operation is invalid (for example, a pop
on an empty stack or an inc
when there are fewer than k
elements), you must insert the minimum number of push
operations (with the value 1
) before that operation so that the sequence becomes valid.
Formally, if at any point a pop
operation is encountered while the stack is empty, you must first insert a push 1
operation to correct it. Similarly, if an inc k x
operation is encountered and the current stack size is less than k
, you must insert exactly k - |stack|
push 1
operations before the inc
operation. The goal is to determine the minimum number of push operations inserted and produce the corrected sequence of operations.
Note that the formula used to determine the number of pushes needed when processing an inc
operation is: $$\text{missing pushes} = k - |stack|$$ where \(|stack|\) is the current size of the stack.
inputFormat
The input is provided via stdin and has the following format:
- The first line contains an integer
n
representing the number of operations in the sequence. - The next
n
lines each contain a string describing an operation. Each operation is one of the following forms:push x
wherex
is an integer (1 ≤ x ≤ 109).pop
inc k x
wherek
(1 ≤ k ≤ current stack size) andx
are integers.
outputFormat
Output the result to stdout with the following format:
- The first line is an integer representing the minimum number of additional
push
operations inserted. - Each subsequent line prints one operation from the corrected sequence, in the order they are executed.
3
push 1
pop
push 2
0
push 1
pop
push 2
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