Submission #109547

#	Time	Username	Problem	Language	Result	Execution time	Memory
109547		PeppaPig	Boat (APIO16_boat)	C++14	0 / 100	11 ms	2304 KiB

boat

#include <bits/stdc++.h>

#define long long long

using namespace std;

const int N = 505;
const int M = 1e9+7;

long fac[N], 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;
}

void pre_process() {
    fac[0] = inv[0] = 1;
    for(int i = 1; i < N; i++) fac[i] = (fac[i-1] * i) % M;
    for(int i = 1; i < N; i++) inv[i] = modpow(fac[i], M-2);
}

long ncr(int n, int r) { return fac[n] * (inv[r] * inv[n-r] % M) % M; }

int n, a[N], b[N];
long dp[N][N];
vector<int> coord;

int main() {
    pre_process();
    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 < coord.size(); i++) dp[0][i] = 1;
    for(int i = 1; i <= n; i++) {
        for(int j = a[i]; j < b[i]; j++) for(int k = i-1, cnt = 1; ~k; k--) {
            dp[i][j] += (ncr(coord[j] - coord[j-1] + cnt - 1, cnt) * dp[k][j-1]) % M;
            dp[i][j] %= M;
            if(a[k] <= j && j < b[k]) ++cnt;
        }
        for(int j = 1; j < coord.size(); 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][coord.size()-1]) % M;
    printf("%lld\n", ans);

    return 0;
}

Compilation message (stderr)

boat.cpp: In function 'int main()':
boat.cpp:47:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i = 0; i < coord.size(); i++) dp[0][i] = 1;
                    ~~^~~~~~~~~~~~~~
boat.cpp:54:26: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int j = 1; j < coord.size(); j++) dp[i][j] = (dp[i][j] + dp[i][j-1]) % M;
                        ~~^~~~~~~~~~~~~~
boat.cpp:35:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d", &n);
     ~~~~~^~~~~~~~~~
boat.cpp:37:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d %d", a+i, b+i);
         ~~~~~^~~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 9
• Subtask 2: 0 / 22
• Subtask 3: 0 / 27
• Subtask 4: 0 / 42