UVa 301 - Transportation

枚举子集+回溯。枚举子集时，需要在每一次递归的过程中进行条件判断，而不能按一般情况放到最后进行判断。

代码如下：

#include <iostream>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <cmath>
using namespace std;
int n, m, num, _max, cal[8];
struct point
{
    int start, des, ticket;
} po[24];
int judge(int cur)
{
    int end = po[cur].des;
    for(int i = po[cur].start; i < end; i++)
    {
        cal[i] += po[cur].ticket;
        if(cal[i] > n)
            return 0;
    }
    return 1;
}
void DFS(int cur, int sum)
{
    if(cur == num)
    {
        if(_max < sum)
            _max = sum;
        return ;
    }
    int save[8];
    DFS(cur + 1, sum);
    memcpy(save, cal, sizeof(save));
    if(judge(cur))
        DFS(cur + 1, sum + po[cur].ticket * (po[cur].des - po[cur].start));
    memcpy(cal, save, sizeof(save));
}
int main()
{
#ifdef test
    freopen("sample.txt", "r", stdin);
#endif
    while(scanf("%d%d%d", &n, &m, &num))
    {
        if(!n && !m && !num)
            break;
        for(int i = 0; i < num; i++)
            scanf("%d%d%d", &po[i].start, &po[i].des, &po[i].ticket);
        _max = 0;
        DFS(0, 0);
        printf("%d\n", _max);
    }
    return 0;
}