[洛谷] P1515 旅行

dfs 递推 都是15ms

递推:

//#pragma GCC optimize(2)
#include <cstdio>
#include <iostream>
#include <cstdlib>
#include <cmath>
#include <cctype>
#include <string>
#include <cstring>
#include <algorithm>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <ctime>
#include <vector>
#include <fstream>
#include <list>
#include <iomanip>
#include <numeric>
using namespace std;
typedef long long ll;

const int MAXN = 1e6 + 10;

int arr[MAXN] = {0,990,1010,1970,2030,2940,3060,3930,4060,4970,5030,5990,6010,7000};

int dp[MAXN] = {0};

int flag = 14, a, b, n, ans = 0;

int main()
{
    //ios::sync_with_stdio(false);

    //cin.tie(0);     cout.tie(0);

    cin>>a>>b>>n;

    for(int i = flag; i < flag + n; i++)
        cin>>arr[i];

    flag += n;

    sort(arr, arr + flag);

    int i;
    for(i = 0; arr[i] <= b; i++)
    {
        if(arr[i] >= a && arr[i] <= b)
            dp[i]++;
    }

    for(i = 0; i < flag; i++)
    {
        for(int j = i; j >= 0; j--)
        {
            if(arr[i] - arr[j] >= a && arr[i] - arr[j] <= b)
                dp[i] += dp[j];
        }
    }

    cout<<dp[flag - 1]<<endl;

    return 0;
}

2.dfs

//#pragma GCC optimize(2)
#include <cstdio>
#include <iostream>
#include <cstdlib>
#include <cmath>
#include <cctype>
#include <string>
#include <cstring>
#include <algorithm>
#include <stack>
#include <queue>
#include <set>
#include <map>
#include <ctime>
#include <vector>
#include <fstream>
#include <list>
#include <iomanip>
#include <numeric>
using namespace std;
typedef long long ll;

const int MAXN = 1e6 + 10;

int arr[MAXN] = {0,990,1010,1970,2030,2940,3060,3930,4060,4970,5030,5990,6010,7000};

int flag = 14, a, b, n, ans = 0;

void dfs(int now)
{
    if(now >= 7000)
    {
        ans++;
        return ;
    }

    for(int i = 0; i < flag; i++)
    {
        if(arr[i] - now >= a && arr[i] - now <= b)
        {
            dfs(arr[i]);
        }
    }
        
}

int main()
{
    //ios::sync_with_stdio(false);

    //cin.tie(0);     cout.tie(0);

    cin>>a>>b>>n;

    for(int i = flag; i < flag + n; i++)
        cin>>arr[i];

    flag += n;

    sort(arr, arr + flag);

    dfs(0);

    cout<<ans<<endl;

    return 0;
}