包对的

#include <bits/stdc++.h>
using namespace std;

vector<vector<int>> graph;
vector<int> color;

bool dfs(int node, int c) {
color[node] = c;
for (int neighbor : graph[node]) {
if (color[neighbor] == -1) {
if (!dfs(neighbor, 1 - c)) return false;
} else if (color[neighbor] == c) {
return false;
}
}
return true;
}

int main() {
int n;
cin >> n;
vector<int> a(n);
for (int i = 0; i < n; i++) {
cin >> a[i];
}

vector<int> f(n + 1);
f[n] = n + 1;
for (int i = n - 1; i >= 0; i--) {
    f[i] = min(a[i], f[i + 1]);
}

graph.resize(n);
for (int i = 0; i < n; i++) {
    for (int j = i + 1; j < n; j++) {
        if (a[i] < a[j] && f[j + 1] < a[i]) {
            graph[i].push_back(j);
            graph[j].push_back(i);
        }
    }
}

color.assign(n, -1);
for (int i = 0; i < n; i++) {
    if (color[i] == -1) {
        if (!dfs(i, 0)) {
            cout << 0;
            return 0;
        }
    }
}

vector<int> s1, s2;
int cur = 1;
int i = 0;
vector<char> res;

while (cur <= n) {
    if (!s1.empty() && s1.back() == cur) {
        s1.pop_back();
        res.push_back('b');
        cur++;
    } else if (!s2.empty() && s2.back() == cur) {
        s2.pop_back();
        res.push_back('d');
        cur++;
    } else if (i < n && color[i] == 0) {
        s1.push_back(a[i]);
        res.push_back('a');
        i++;
    } else if (i < n && color[i] == 1) {
        s2.push_back(a[i]);
        res.push_back('c');
        i++;
    } else {
        cout << 0;
        return 0;
    }
}

for (int idx = 0; idx < res.size(); idx++) {
    if (idx > 0) cout << " ";
    cout << res[idx];
}

return 0;

}