【非原创】codeforces

学习博客：戳这里

附本人代码：

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const int maxn = 1e5 + 10;
const ll mod = 998244353;
set<int>nu[maxn], rol[2];
int a[maxn];
ll dp[maxn][222][3];
int main() {
    int n;
    scanf("%d", &n);
    for(int i = 1; i <= n; ++i) {
        scanf("%lld", a+i);
    }
    //处理边界
    if(a[1] == -1) {
        for(int i = 1; i <= 200; ++i) {
                dp[1][i][0] = 1ll;
        }
    } else {
            dp[1][a[1]][0] = 1ll;
    }
    for(int i = 2; i <= n; ++i) {
        ll sum = 0;
        int len = 200;
        if(a[i] != -1) len = a[i];
        for(int j = 1; j <= len; ++j) { // >
            if(a[i] == -1 || j == a[i])
            dp[i][j][0] = (dp[i][j][0] + sum) % mod;
            for(int k = 0; k < 3; ++k) {
                sum = (sum + dp[i - 1][j][k]) % mod;
            }
        }
        for(int j = 1; j <= len; ++j) { // ==
                for(int k = 0; k < 3; ++k) {
                    if(a[i] == -1 || j == a[i])
                    dp[i][j][1] = (dp[i][j][1] + dp[i - 1][j][k]) % mod;
                }
        }
        if(i == 2) continue;
        len = 1;
        if(a[i] != -1) len = a[i];
        sum = 0;
        for(int j = 200; j >= len; --j) { // <
            if(a[i] == -1 || j == a[i])
            dp[i][j][2] =(dp[i][j][2] + sum) % mod;
            for(int k = 1; k < 3; ++k) {
                sum = (sum + dp[i - 1][j][k]) % mod;
            }
        }
    }
    ll ans = 0;
    for(int j = 1; j <= 200; ++j) {
        for(int k = 1; k < 3; ++k) {
            if(a[n] == -1 || j == a[n])
            ans = (ans + dp[n][j][k]) % mod;
        }
    }
    printf("%lld
", ans);
    return 0;
}