Submission #516316

#	Time	Username	Problem	Language	Result	Execution time	Memory
516316		PeppaPig	Boat (APIO16_boat)	C++14	100 / 100	581 ms	4384 KiB

boat

#include <bits/stdc++.h>
 
#define long long long
 
using namespace std;
 
const int N = 1005;
const int M = 1e9+7;
 
long inv[N];
 
long modpow(long a, long b) {
    long ret = 1;
    for( ; b; b >>= 1) {
        if(b & 1) ret = (ret * a) % M;
        a = (a * a) % M;
    }
    return ret;
}
 
int n, a[N], b[N];
long dp[N][N];
vector<int> coord;
 
int main() {
    for(int i = 1; i < N; i++) inv[i] = modpow(i, M-2);
    scanf("%d", &n);
    for(int i = 1; i <= n; i++) {
        scanf("%d %d", a+i, b+i);
        coord.emplace_back(a[i]);
        coord.emplace_back(++b[i]);
    }
    sort(coord.begin(), coord.end());
    coord.resize(unique(coord.begin(), coord.end()) - coord.begin());
    for(int i = 1; i <= n; i++) {
        a[i] = lower_bound(coord.begin(), coord.end(), a[i]) - coord.begin() + 1;
        b[i] = lower_bound(coord.begin(), coord.end(), b[i]) - coord.begin() + 1;
    }
    for(int i = 0; i < N; i++) dp[0][i] = 1;
    for(int i = 1; i <= n; i++) {
        for(int j = a[i]; j < b[i]; j++) {
            long p = coord[j] - coord[j-1], cnt = 1;
            for(int k = i-1; ~k; k--) {
                dp[i][j] = (dp[i][j] + (p * dp[k][j-1]) % M) % M;
                if(a[k] <= j && j < b[k]) {
                    ++cnt;
                    p = (p * (coord[j] - coord[j-1] + cnt - 1)) % M;
                    p = (p * inv[cnt]) % M;
                }
            }
        }
        for(int j = 1; j < N; j++) dp[i][j] = (dp[i][j] + dp[i][j-1]) % M;
    }
    long ans = 0;
    for(int i = 1; i <= n; i++) ans = (ans + dp[i][N-1]) % M;
    printf("%lld\n", ans);
 
    return 0;
}

Compilation message (stderr)

boat.cpp: In function 'int main()':
boat.cpp:27:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   27 |     scanf("%d", &n);
      |     ~~~~~^~~~~~~~~~
boat.cpp:29:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   29 |         scanf("%d %d", a+i, b+i);
      |         ~~~~~^~~~~~~~~~~~~~~~~~~

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