HDU 1160 FatMouse's Speed

/**
*   Author : johnsondu
*   time : 2013-4-7
*   Type: DP, I want to really understand it
*   problem: FatMouse's Speed
*   url: http://acm.hdu.edu.cn/showproblem.php?pid=1160
*/

#include <iostream>
#include <cstdio>
#include <cmath>
#include <vector>
#include <cstring>
#include <algorithm>
using namespace std ;

#define max(a, b) (a > b ? a : b)
struct Node
{
    int w, s ;
    int idx ;
}node[1005] ;
int n, dp[1005] ;

bool cmp (const Node &a, const Node &b)
{
    if (a.w != b.w)
        return a.w < b.w ;
    return a.s > b.s ;
}

int main ()
{
    int i, j ;
    //freopen ("data.txt", "r", stdin) ;
    n = 0 ;
    while (scanf ("%d%d", &node[n].w, &node[n].s) != EOF)
    {
        node[n].idx = n ;
        n ++ ;
    }
    sort (node, node + n, cmp) ;

    for (i = 0; i < n; i ++)
        dp[i] = 1 ;

    int num = 0 ;
    for (i = 0; i < n-1; i ++)
    {
        for (j = i+1; j < n; j ++)
            if (node[j].w > node[i].w && node[j].s < node[i].s)
            {
                dp[j] = max(dp[i]+1, dp[j]) ;           //状态转移方程
                if (dp[j] > dp[num])
                    num = j ;                           //记录最大值下标
            }
    }
    printf ("%d\n", dp[num]) ;
    int tp = num ;
    vector<int> mm ;
    mm.push_back(num) ;
    for (i = num-1; i >= 0; i --)   //寻找路径
        if (dp[num] == dp[i] + 1)
        {
            mm.push_back(i) ;
            num = i ;
        }
    for (i = dp[tp]-1; i >= 0; i --)
        printf ("%d\n", node[mm[i]].idx+1) ;

    return 0 ;
}