Codeforces Round #479 (Div. 3) F. Consecutive Subsequence

Codeforces Round #479 (Div. 3) F. Consecutive Subsequence

Tag: DP

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topic link

analyze

Although it is not difficult dp, I thought it was difficult to put it in the position of question F. I still thought it was complicated and it took a long time to get it out, and I also encountered a std::unordered_mappit. There is a special card for a group of data on the CF, unordered_mapand then it is tle.
Because it unordered_mapis hash storage, the same hash value will be placed in a bucket, but the complexity of searching in the bucket is \(O(n)\) . The following optimization method was found on codeforces

unordered_map<int,int>mp;
mp.reserve(1024);
mp.max_load_factor(0.25);

That way it won't be troll.
See the following two links for specific principles:
http://codeforces.com/blog/entry/21853
http://en.cppreference.com/w/cpp/container/unordered_map/reserve

code

#include <iostream>
#include <cstring>
#include <algorithm>
#include <vector>
#include <cstdio>
#include <map>
#include <unordered_map>
using namespace std;
const int maxn=200050;
int a[maxn];
unordered_map<int,int> dp;
int main(){
    dp.reserve(maxn);
    dp.max_load_factor(0.25);

    int n;
    scanf("%d", &n);
    int M=0,e=0;
    for(int i = 0; i < n; ++i){
        scanf("%d", a+i);
        int& u=dp[a[i]];
        if(dp.count(a[i]-1)) u=max(u,dp[a[i]-1]+1);
        else u=1;
        if(u>M){
            M=u;
            e=a[i];
        }
    }
    int b=e-M+1;
    cout << M << endl;
    for(int i = 0; i < n; ++i){
        if(a[i]==b){
            printf("%d ", i+1);
            b++;
        }
    }
    return 0;
}