Problem link: http://codeforces.com/contest/431/problem/C
Simple recursion with memoization works.
Code is self explanatory
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| #include <vector> | |
| #include <list> | |
| #include <map> | |
| #include <set> | |
| #include <deque> | |
| #include <queue> | |
| #include <stack> | |
| #include <bitset> | |
| #include <algorithm> | |
| #include <functional> | |
| #include <numeric> | |
| #include <utility> | |
| #include <sstream> | |
| #include <iostream> | |
| #include <iomanip> | |
| #include <cstdio> | |
| #include <cmath> | |
| #include <cstdlib> | |
| #include <ctime> | |
| #include <cstring> | |
| #include <climits> | |
| #include <stdlib.h> | |
| #include <stdio.h> | |
| using namespace std; | |
| #define REP(i,n) for(int i=0; i<n; i++) | |
| #define FOR(i,st,end) for(int i=st;i<end;i++) | |
| #define db(x) cout << (#x) << " = " << x << endl; | |
| #define mp make_pair | |
| #define pb push_back | |
| #define mod 1000000007 | |
| typedef long long int ll; | |
| int k,d,n; | |
| ll dp[105][2]; | |
| ll solve(int x,int f){ | |
| if(dp[x][f]!=-1){ | |
| return dp[x][f]; | |
| } | |
| if(x>n) | |
| dp[x][f]=0; | |
| else if((x==n)&&f) | |
| dp[x][f]=1; | |
| else{ | |
| ll ret=0; | |
| for(int i=1;i<=k;i++){ | |
| if(x+i<=n){ | |
| ret+=solve(x+i,f||(i>=d)?1:0); | |
| ret%=mod; | |
| } | |
| } | |
| dp[x][f]=ret; | |
| } | |
| return dp[x][f]; | |
| } | |
| int main(){ | |
| REP(i,105){ | |
| dp[i][0]=-1; | |
| dp[i][1]=-1; | |
| } | |
| scanf("%d%d%d",&n,&k,&d); | |
| ll ret=0; | |
| for(int i=1;i<=k;i++){ | |
| ret+=solve(i,(i>=d)?1:0); | |
| ret%=mod; | |
| } | |
| cout<<ret; | |
| } |
coding hangover 