Submission #1092156

#	Time	Username	Problem	Language	Result	Execution time	Memory
1092156		khanhgng	Mountains (NOI20_mountains)	C++14	100 / 100	134 ms	15556 KiB

Mountains

#pragma GCC optimize ("O3")
#include<bits/stdc++.h>
#define fi first
#define se second
#define ll long long
#define ld long double
#define pii pair<int,int>
#define SZ(x) ((int)(x.size()))
#define bit(i,x) ((x>>i)&1)
#define pb push_back
#define FOR(i,a,b) for(int i=(a);i<=(b);++i)
#define FORD(i,a,b) for(int i=(a);i>=(b);--i)
#define task "mountains"
#define int long long

using namespace std;

mt19937 rd(chrono::steady_clock::now().time_since_epoch().count());
ll Rand(ll l,ll r){assert(l<=r);return uniform_int_distribution<ll>(l,r)(rd);}

const int MAXn=5e5+7;
const int MOD=1e9+7;
const ll oo = 1e18;
const ll BASE=3137LL;

int n,a[MAXn],dp[MAXn],res;

struct FenwickTree{
    int f[MAXn];
    int N;
    void init(int n){FOR(i,1,n)f[i]=0;N=n;}
    void upd(int idx,int val){
        for(idx;idx<=N;idx+=(idx&-idx)){
            f[idx]+=val;
        }
    }
    int get(int idx){
        int ans=0;
        for(idx;idx>=1;idx-=(idx&-idx)){
            ans+=f[idx];
        }
        return ans;
    }
}ft;

void solution(){
    cin>>n;
    vector<int>zip;
    FOR(i,1,n)cin>>a[i],zip.pb(a[i]);
    sort(zip.begin(),zip.end());
    zip.resize(unique(zip.begin(),zip.end())-zip.begin());
    FOR(i,1,n)a[i]=lower_bound(zip.begin(),zip.end(),a[i])-zip.begin()+1;
    ft.init(n);
    FOR(i,1,n){
        dp[i]=ft.get(a[i]-1);
        ft.upd(a[i],1);
    }
    ft.init(n);
    FORD(i,n,1){
        res+=dp[i]*ft.get(a[i]-1);
        ft.upd(a[i],1);
    }
    cout<<res;

}

int32_t main(){
    if(fopen(task".inp","r")){freopen(task".inp","r",stdin);freopen(task".out","w",stdout);}
    ios_base::sync_with_stdio(0);cin.tie(0);
    int ntest=1;//cin>>ntest;
    while(ntest--){solution();}
    cerr<<"\n"<<1.0*clock()/CLOCKS_PER_SEC<<"s ";
}

Compilation message (stderr)

Mountains.cpp: In member function 'void FenwickTree::upd(long long int, long long int)':
Mountains.cpp:33:13: warning: statement has no effect [-Wunused-value]
   33 |         for(idx;idx<=N;idx+=(idx&-idx)){
      |             ^~~
Mountains.cpp: In member function 'long long int FenwickTree::get(long long int)':
Mountains.cpp:39:13: warning: statement has no effect [-Wunused-value]
   39 |         for(idx;idx>=1;idx-=(idx&-idx)){
      |             ^~~
Mountains.cpp: In function 'int32_t main()':
Mountains.cpp:68:38: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   68 |     if(fopen(task".inp","r")){freopen(task".inp","r",stdin);freopen(task".out","w",stdout);}
      |                               ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
Mountains.cpp:68:68: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   68 |     if(fopen(task".inp","r")){freopen(task".inp","r",stdin);freopen(task".out","w",stdout);}
      |                                                             ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 2 / 2
• Subtask 2: 4 / 4
• Subtask 3: 9 / 9
• Subtask 4: 36 / 36
• Subtask 5: 28 / 28
• Subtask 6: 9 / 9
• Subtask 7: 12 / 12