using Stack sortable property, just verify if the input traversal vector does not contain the permutation pattern 231: three elements x, y, and z, appearing in the input in that respective order, with z < x < y.

```
int Solution::solve(vector<int> &A) {
if(A.size() < 1) return 1;
stack<int> st;
int rootNodeVal = INT_MIN;
for(auto it: A) {
if(it < rootNodeVal) return 0;
while(!st.empty() && st.top() < it) {
rootNodeVal = st.top();
st.pop();
}
st.push(it);
}
return 1;
}
```