Submission #118609

#	Time	Username	Problem	Language	Result	Execution time	Memory
118609		pzdba	Boat (APIO16_boat)	C++14	100 / 100	576 ms	4512 KiB

boat

#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
const int mod = 1e9+7;
vector<int> h;
int a[505], b[505], l[1005];
LL dp[505][1005];
LL inv[505];
LL go(LL a, LL b){
    LL ans=1;
    while(b){
        if(b%2) ans=ans*a%mod;
        a=a*a%mod;
        b/=2;
    }
    return ans;
}

int main(){
    int n;
    scanf("%d", &n);
    for(int i=0;i<=n;i++) inv[i] = go(i, mod-2);

    for(int i=1;i<=n;i++){
        scanf("%d%d", &a[i], &b[i]);
        h.push_back(a[i]-1);
        h.push_back(b[i]);
    }   
    sort(h.begin(), h.end());
    h.erase(unique(h.begin(), h.end()), h.end());
    for(int i=1;i<=n;i++){
        a[i] = lower_bound(h.begin(), h.end(), a[i]-1) - h.begin() + 1;
        b[i] = lower_bound(h.begin(), h.end(), b[i]) - h.begin() + 1;
    }
    l[1] = h[0];
    for(int i=2;i<=h.size();i++) l[i] = h[i-1] - h[i-2];
    for(int i=1;i<=n;i++){
        for(int j=1;j<=h.size();j++){
            if(i == 1){
                if(a[i] < j && j <= b[i]) dp[i][j] = (dp[i][j] + l[j])%mod;
            }
            else{
                if(a[i] < j && j <= b[i]){
                    dp[i][j] = (dp[i][j] + l[j] + l[j]*dp[i-1][j-1])%mod;
                    int cnt = 1;
                    LL sum = l[j]-1;
                    for(int k=i-1;k>=1;k--){
                        if(a[k] < j && j <= b[k]){
                            cnt++;
                            sum = sum*(l[j]+cnt-2)%mod*inv[cnt]%mod;
                            dp[i][j] = (dp[i][j] + sum + sum*dp[k-1][j-1])%mod;
                        }
                    }
                }
            }
            dp[i][j] = (dp[i][j] + dp[i][j-1] + dp[i-1][j] - dp[i-1][j-1] + mod)%mod;
        }
    }
    printf("%lld\n", dp[n][h.size()]);
}

Compilation message (stderr)

boat.cpp: In function 'int main()':
boat.cpp:36:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=2;i<=h.size();i++) l[i] = h[i-1] - h[i-2];
                 ~^~~~~~~~~~
boat.cpp:38:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int j=1;j<=h.size();j++){
                     ~^~~~~~~~~~
boat.cpp:21:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d", &n);
     ~~~~~^~~~~~~~~~
boat.cpp:25:14: 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: 9 / 9
• Subtask 2: 22 / 22
• Subtask 3: 27 / 27
• Subtask 4: 42 / 42