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.
Note:
0 <= pushed.length == popped.length <= 1000 0 <= pushed[i], popped[i] < 1000 pushed is a permutation of popped. pushed and popped have distinct values.
// 12ms, 50%
class Solution {
public:
bool validateStackSequences(vector<int>& pushed, vector<int>& popped) {
stack<int> stk;
int i = 0, j = 0;
for(; i < pushed.size(); i++) {
stk.push(pushed[i]);
while (!stk.empty() && j < popped.size() && (stk.top() == popped[j])) {
j++;
stk.pop();
}
}
return stk.empty() && j == popped.size();
}
};