README.md

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.

Solutions (Ruby)

1. Solution

# @param {Integer[]} pushed
# @param {Integer[]} popped
# @return {Boolean}
def validate_stack_sequences(pushed, popped)
    stack = []
    i = 0

    for val in pushed
        stack.push(val)
        while i < popped.length and stack.last == popped[i]
            stack.pop
            i += 1
        end
    end

    return stack.empty?
end

Solutions (Rust)

1. Solution

impl Solution {
    pub fn validate_stack_sequences(pushed: Vec<i32>, popped: Vec<i32>) -> bool {
        let mut stack = vec![];
        let mut i = 0;

        for val in pushed {
            stack.push(val);
            while i < popped.len() && *stack.last().unwrap_or(&-1) == popped[i] {
                stack.pop();
                i += 1;
            }
        }

        stack.is_empty()
    }
}