class Solution {
public:
vector<int> seq;
bool verifySequenceOfBST(vector<int> sequence) {
seq = sequence;
return dfs(0, seq.size()-1);
}
bool dfs(int l, int r){
if(l >= r) return true;
int root = seq[r];
int k = l;
while(k < r && seq[k]<root) k++;
for(int i = k; i < r; i++)
if(seq[i] < root)
return false;
return dfs(l, k-1) && dfs(k, r-1);
}
};