830. 单调栈

https://www.acwing.com/problem/content/submission/code_detail/7415280/

AcWing/830/830.cpp

@@ -0,0 +1,22 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+int n, a;
+stack<int> st;
+
+int main() {
+    cin >> n;
+    for (int i = 0; i < n; i++) {
+        cin >> a;
+        while (!st.empty() && st.top() >= a) st.pop();
+        if (st.empty()) {
+            cout << -1 << ' ';
+        } else {
+            cout << st.top() << ' ';
+        }
+        st.push(a);
+    }
+    cout << endl;
+    return 0;
+}