51NOD 1201 整数划分

http://www.51nod.com/onlineJudge/questionCode.html#!problemId=1201

一样的思路

http://www.cnblogs.com/liuweimingcprogram/p/6072869.html

由于其是先算dp[1][1--n]的，故需要用ans数组存

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <algorithm>
#define IOS ios::sync_with_stdio(false)
using namespace std;
#define inf (0x3f3f3f3f)
typedef long long int LL;

#include <iostream>
#include <sstream>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <string>
#include <time.h>
const int MOD = 1e9 + 7;
const int maxn = 50000 + 20;
int dp[2][maxn];
const int N = maxn - 20;
int ans[maxn];
void work() {
    dp[0][0] = 1;
    int now = 0;
    int all = 0;
    for (int i = 1; i <= N; ++i) {
        if (i * (i + 1) / 2 > N) break;
        for (int j = i * (i + 1) / 2; j <= N; ++j) {
            dp[now][j] = (dp[now][j - i] + dp[!now][j - i]) % MOD;
            ans[j] += dp[now][j];
            ans[j] %= MOD;
            all++;
        }
        memset(dp[!now], 0, sizeof dp[!now]);
//        all += maxn;
        now = !now;
    }
//    cout << all << endl;
////    cout << ans[N] << endl;
//    for (int i = 1; i <= 20; ++i) {
//        cout << ans[i] << endl;
//    }
    int n;
    scanf("%d", &n);
    printf("%d
", ans[n]);
}

int main() {
#ifdef local
    freopen("data.txt","r",stdin);
#endif
//    LL t = time(NULL);
//    cout << t << endl;
    work();
//    LL tt = time(NULL);
//    cout << tt  << endl;
    return 0;
}