Submission #494896

#	Time	Username	Problem	Language	Result	Execution time	Memory
494896		XII	Boat (APIO16_boat)	C++17	100 / 100	528 ms	2456 KiB

boat

#include <bits/stdc++.h>
using namespace std;

using ll = long long;

#define fi first
#define se second
#define mp make_pair
#define eb emplace_back
#define ALL(x) (x).begin(), (x).end()

#define FOR(i, a, b) for(int i = (a); i < (b); ++i)
#define FORU(i, a, b) for(int i = (a); i <= (b); ++i)
#define FORD(i, a, b) for(int i = (a); i >= (b); --i)

#define IOS cin.tie(0)->sync_with_stdio(false);
#define PROB "DUT03TEAMS"
void Fi(){
    if(fopen(PROB".inp", "r")){
        freopen(PROB".inp", "r", stdin);
        freopen(PROB".out", "w", stdout);
    }
}

const int N = 500 + 1;
const int MOD = 1e9 + 7;
int a[N], b[N], n, m;
int dp[N][N << 1];
int X[N << 1];
int inv[N];

int add(const int &a, const int &b){
    return (a + b >= MOD ? a + b - MOD : a + b);
}

int mul(const int &a, const int &b){
    return (1LL * a * b) % MOD;
}

void compress(){
    sort(X + 1, X + m + 1);
    m = unique(X + 1, X + m + 1) - X;
    FORU(i, 1, n){
        a[i] = lower_bound(X + 1, X + m, a[i]) - X;
        b[i] = lower_bound(X + 1, X + m, b[i]) - X;
//        cout << a[i] << " " << b[i] << "\n";
    }
    m -= 2;
//    cout << m << "\n";
}

int main(){
    IOS;
    Fi();
    cin >> n;
    FORU(i, 1, n){
        cin >> a[i] >> b[i];
        X[++m] = a[i];
        X[++m] = ++b[i];
    }
    compress();

    inv[1] = 1;
    FORU(i, 2, n){
        inv[i] = mul(MOD - MOD / i, inv[MOD % i]);
    }

    int ans = 0;
    FORU(j, 0, m) dp[0][j] = 1;
    FORU(i, 1, n){
        FOR(j, a[i], b[i]){
            int len = X[j + 1] - X[j];
            int C = len, cnt = 1;
            FORD(k, i - 1, 0){
                dp[i][j] = add(dp[i][j], mul(dp[k][j - 1], C));
                if(a[k] <= j && j < b[k]){
                    ++cnt;
                    C = mul(mul(C, len + cnt - 1), inv[cnt]);
                }
            }
        }
        FORU(j, 2, m) dp[i][j] = add(dp[i][j], dp[i][j - 1]);
        ans = add(ans, dp[i][m]);
    }
    cout << ans;
    return 0;
}

Compilation message (stderr)

boat.cpp: In function 'void Fi()':
boat.cpp:20:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   20 |         freopen(PROB".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
boat.cpp:21:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   21 |         freopen(PROB".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 9 / 9
• Subtask 2: 22 / 22
• Subtask 3: 27 / 27
• Subtask 4: 42 / 42