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 ofpushed
.
Solution:
class Solution {
public boolean validateStackSequences(int[] pushed, int[] popped) {
int N = pushed.length;
Stack<Integer> stack = new Stack();
int j = 0;
for (int x: pushed) {
stack.push(x);
while (!stack.isEmpty() && j < N && stack.peek() == popped[j]) {
stack.pop();
j++;
}
}
return j == N;
}
}