Codeforces Round #107 (Div. 2)

D题

并查集+组合

#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;
#define MOD 1000000007
int o[2001];
int find(int x)
{
    int t,r;
    t = x;
    while(x != o[x])
    x = o[x];
    while(x != t)
    {
        r = o[t];
        o[t] = x;
        t = r;
    }
    return x;
}
void merge(int x,int y)
{
    x = find(x);
    y = find(y);
    if(x != y)
    o[x] = y;
}
int main()
{
    int i,j,n,m,k,ans = 0;
    scanf("%d%d%d",&n,&m,&k);
    for(i = 1;i <= n;i ++)
    o[i] = i;
    for(i = 1;i <= n;i ++)
    {
        if(k%2 == 0)
        {
            if(2*i < k) continue;
            if(i + k/2 > n) continue;
            for(j = 0;j < k/2;j ++)
            {
                merge(i-j,i+1+j);
            }
        }
        else
        {
            if(2*i-1 < k) continue;
            if(i + k/2 > n) continue;
            for(j = 0;j < k/2;j ++)
            merge(i-1-j,i+1+j);
        }
    }
    for(i = 1;i <= n;i ++)
    {
        if(find(i) == i)
        ans ++;
    }
    int sd = 1;
    for(i = 1;i <= ans;i ++)
    sd = ((__int64)sd*m)%MOD;
    printf("%d
",sd);
    return 0;
}