F - Pre-order and In-order

https://atcoder.jp/contests/abc255/submissions/32427435

AtCoder/ABC255/F/F.cpp

@@ -0,0 +1,58 @@
+#include <iostream>
+#include <algorithm>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 2e5 + 5;
+
+int n, cnt, pre[N], in[N];
+std::pair<int, int> tr[N];
+
+int dfs(int l, int r) {
+    if (l > r) return 0;
+
+    if (cnt > n) {
+        cout << -1 << endl;
+
+        exit(0);
+    }
+
+    int root = pre[++cnt];
+
+    tr[root].first = dfs(l, in[root] - 1);
+    tr[root].second = dfs(in[root] + 1, r);
+
+    return root;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n;
+
+    for (int i = 1; i <= n; i++) {
+        cin >> pre[i];
+    }
+
+    for (int i = 1, x; i <= n; i++) {
+        cin >> x;
+        in[x] = i;
+    }
+
+    if (pre[1] != 1) {
+        cout << -1 << endl;
+
+        exit(0);
+    }
+
+    dfs(1, n);
+
+    for (int i = 1; i <= n; i++) {
+        cout << tr[i].first << ' ' << tr[i].second << endl;
+    }
+
+    return 0;
+}