Codeforces 1144G Two Merged Sequences dp

Posted 2021-11-25 cjlhy

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 + 7;
const int inf = 0x3f3f3f3f;
const LL INF = 0x3f3f3f3f3f3f3f3f;
const int mod = 1000000007;
const double eps = 1e-6;
const double PI = acos(-1);

int n, a[N], ans[N];
int dp[N][2], path[N][2];

int main() {
    scanf("%d", &n);
    for(int i = 1; i <= n; i++) scanf("%d", &a[i]);
    for(int i = 1; i <= n; i++)
        dp[i][0] = -inf, dp[i][1] = inf;
    dp[1][0] = 1e9 + 1;
    dp[1][1] = -1;
    for(int i = 1; i < n; i++) {
        if(dp[i][0] > -inf) {
            if(a[i + 1] > a[i]) {
                if(dp[i][0] > dp[i + 1][0]) {
                    dp[i + 1][0] = dp[i][0];
                    path[i + 1][0] = 0;
                }
            }
            if(a[i + 1] < dp[i][0]) {
                if(a[i] < dp[i + 1][1]) {
                    dp[i + 1][1] = a[i];
                    path[i + 1][1] = 0;
                }
            }
        }
        if(dp[i][1] < inf) {
            if(a[i + 1] < a[i]) {
                if(dp[i][1] < dp[i + 1][1]) {
                    dp[i + 1][1] = dp[i][1];
                    path[i + 1][1] = 1;
                }
            }
            if(a[i + 1] > dp[i][1]) {
                if(a[i] > dp[i + 1][0]) {
                    dp[i + 1][0] = a[i];
                    path[i + 1][0] = 1;
                }
            }
        }
    }
    if(dp[n][0] > -inf) {
        puts("YES");
        int now = 0;
        for(int i = n; i >= 1; i--) {
            ans[i] = now;
            now = path[i][now];
        }
        for(int i = 1; i <= n; i++) printf("%d ", ans[i]);
        puts("");
    } else if(dp[n][1] < inf) {
        puts("YES");
        int now = 1;
        for(int i = n; i >= 1; i--) {
            ans[i] = now;
            now = path[i][now];
        }
        for(int i = 1; i <= n; i++) printf("%d ", ans[i]);
        puts("");
    } else {
        puts("NO");
    }
    return 0;
}

/*
*/