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
.
Companies:
Amazon, Microsoft, tiktok
Related Topics:
Array, Stack, Simulation
// OJ: https://leetcode.com/problems/validate-stack-sequences/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(N)
class Solution {
public:
bool validateStackSequences(vector<int>& pushed, vector<int>& popped) {
stack<int> s;
int p = 0;
for (int i : pushed) {
s.push(i);
while (s.size() && s.top() == popped[p]) {
s.pop();
++p;
}
}
return s.empty();
}
};
// OJ: https://leetcode.com/problems/validate-stack-sequences/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(1) extra space.
class Solution {
public:
bool validateStackSequences(vector<int>& pushed, vector<int>& popped) {
int N = pushed.size(), i = 0, j = 0;
for (int n : pushed) {
pushed[i++] = n;
while (i && pushed[i - 1] == popped[j]) --i, ++j;
}
return i == 0;
}
};