CF1079C Playing Piano

思路：

dp。

实现：

#include <bits/stdc++.h>
using namespace std;
int a[100005], dp[100005][6];
int main()
{
    int n;
    while (cin >> n)
    {
        for (int i = 1; i <= n; i++) cin >> a[i];
        memset(dp, 0, sizeof dp);
        for (int i = 1; i <= 5; i++) dp[1][i] = 1;
        for (int i = 2; i <= n; i++)
        {
            for (int j = 1; j <= 5; j++)
            {
                if (a[i] > a[i - 1])
                {
                    for (int k = 1; k < j; k++)
                    {
                        if (dp[i - 1][k]) dp[i][j] = k;
                    }
                }
                else if (a[i] < a[i - 1])
                {
                    for (int k = j + 1; k <= 5; k++)
                    {
                        if (dp[i - 1][k]) dp[i][j] = k;
                    }
                }
                else
                {
                    for (int k = 1; k <= 5; k++)
                    {
                        if (k != j && dp[i - 1][k]) dp[i][j] = k;
                    }
                }
            }
        }
        bool flg = false;
        int i = 1;
        for ( ; i <= 5; i++)
        {
            if (dp[n][i]) { flg = true; break; }
        }
        if (!flg) cout << "-1" << endl;
        else
        {
            vector<int> v;
            v.push_back(i);
            int now = n;
            while (now >= 2)
            {
                v.push_back(dp[now][i]);
                i = dp[now][i];
                now--;
            }
            for (int i = v.size() - 1; i >= 0; i--) cout << v[i] << " ";
            cout << endl;
        }
    }
    return 0;
}