Codeforces 1144G Two Merged Sequences dp

Two Merged Sequences

感觉是个垃圾题啊， 为什么过的人这么少。。

dp[ i ][ 0 ]表示处理完前 i 个， 第 i 个是递增序列序列里的元素，递减序列的最大值。

dp[ i ][ 1 ]表示处理完前 i 个， 第 i 个是递减序列序列里的元素，递增序列的最小值。

然后随便转移转移顺便记录一下路径就好啦。

#include<bits/stdc++.h>
#define LL long long
#define fi first
#define se second
#define mk make_pair
#define PLL pair<LL, LL>
#define PLI pair<LL, int>
#define PII pair<int, int>
#define SZ(x) ((int)x.size())
#define ull unsigned long long

using namespace std;

const int N = 2e5 + ;
const int inf = 0x3f3f3f3f;
const LL INF = 0x3f3f3f3f3f3f3f3f;
const int mod = ;
const double eps = 1e-;
const double PI = acos(-);

int n, a[N], ans[N];
int dp[N][], path[N][];

int main() {
    scanf("%d", &n);
    for(int i = ; i <= n; i++) scanf("%d", &a[i]);
    for(int i = ; i <= n; i++)
        dp[i][] = -inf, dp[i][] = inf;
    dp[][] = 1e9 + ;
    dp[][] = -;
    for(int i = ; i < n; i++) {
        if(dp[i][] > -inf) {
            if(a[i + ] > a[i]) {
                if(dp[i][] > dp[i + ][]) {
                    dp[i + ][] = dp[i][];
                    path[i + ][] = ;
                }
            }
            if(a[i + ] < dp[i][]) {
                if(a[i] < dp[i + ][]) {
                    dp[i + ][] = a[i];
                    path[i + ][] = ;
                }
            }
        }
        if(dp[i][] < inf) {
            if(a[i + ] < a[i]) {
                if(dp[i][] < dp[i + ][]) {
                    dp[i + ][] = dp[i][];
                    path[i + ][] = ;
                }
            }
            if(a[i + ] > dp[i][]) {
                if(a[i] > dp[i + ][]) {
                    dp[i + ][] = a[i];
                    path[i + ][] = ;
                }
            }
        }
    }
    if(dp[n][] > -inf) {
        puts("YES");
        int now = ;
        for(int i = n; i >= ; i--) {
            ans[i] = now;
            now = path[i][now];
        }
        for(int i = ; i <= n; i++) printf("%d ", ans[i]);
        puts("");
    } else if(dp[n][] < inf) {
        puts("YES");
        int now = ;
        for(int i = n; i >= ; i--) {
            ans[i] = now;
            now = path[i][now];
        }
        for(int i = ; i <= n; i++) printf("%d ", ans[i]);
        puts("");
    } else {
        puts("NO");
    }
    return ;
}

/*
*/