source: https://leetcode.com/problems/validate-stack-sequences/description/
Validate Stack Sequences
Given two integer arrays pushed and popped each with distinct values, return true if this could have been the result of a sequence of push and pop operations on an initially empty stack, or false otherwise.
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:
- 1 <= pushed.length <= 1000
- 0 <= pushed[i] <= 1000
- All the elements of pushed are unique.
- popped.length == pushed.length
- popped is a permutation of pushed.
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class Solution { public boolean validateStackSequences(int[] pushed, int[] popped) { ArrayDeque<Integer> stack = new ArrayDeque<>(); int x = 0; int y = 0; while(x<pushed.length){ \\O(n) stack.push(pushed[x++]); while(!stack.isEmpty() && stack.peek()==popped[y]){ stack.pop(); y++; } } while(y < popped.length){ \\O(n) if(!stack.isEmpty() && stack.peek()==popped[y]){ stack.pop(); y++; } else { return false; } } //System.out.println(stack); return stack.isEmpty(); } } |
Time complexity
O(n)
Space Complexity
o(n)