946. Validate Stack Sequences

Given two sequences pushed and popped with distinct values , return true if and only if this could have been the result of a sequence of push and pop operations on an initially empty stack.

Example 1:

Input: pushed = [1,2,3,4,5], popped = [4,5,3,2,1]
Output: true
Explanation: We might do the following sequence:
push(1), push(2), push(3), push(4), pop() -> 4,
push(5), pop() -> 5, pop() -> 3, pop() -> 2, pop() -> 1

Example 2:

Input: pushed = [1,2,3,4,5], popped = [4,3,5,1,2]
Output: false
Explanation: 1 cannot be popped before 2.

Constraints:

• 0 <= pushed.length == popped.length <= 1000
• 0 <= pushed[i], popped[i] < 1000
• pushed is a permutation of popped.
• pushed and popped have distinct values.

# @lc code=start
using LeetCode
function validate_stack_sequences(pushed::Vector{Int}, popped::Vector{Int})
    return validate_stack_sequences!(copy(pushed), popped)
end
function validate_stack_sequences!(pushed::Vector{Int}, popped::Vector{Int})::Bool
    stack = Int[]
    for num in popped
        while isempty(stack) || last(stack) != num
            isempty(pushed) && return false
            push!(stack, popfirst!(pushed))
        end
        pop!(stack)
    end
    return true
end

# @lc code=end

validate_stack_sequences! (generic function with 1 method)

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