URAL 1078. Segments(DP)

题目链接

找出最高一个线段覆盖吧，很明显的O(n^2)的DP，注意排序的时候按长度排序。WA了一次，没有注意到题目中their endpoints do not coincide，他们的端点不能重合，我还以为输出要顺序有错误。。。得亏又看了遍题目。。

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
struct segment
{
    int x,y,len;
    int num;
}p[501];
int o[501],k[501],q[501];
int cmp(const void *a,const void *b)
{
    return (*(struct segment *)a).len > (*(struct segment *)b).len?1:-1;
}
int main()
{
    int i,j,n,t,max;
    scanf("%d",&n);
    for(i = 0;i <= n-1;i ++)
    {
        scanf("%d%d",&p[i].x,&p[i].y);
        p[i].len = p[i].y-p[i].x;
        p[i].num = i;
    }
    qsort(p,n,sizeof(p[0]),cmp);
    o[0] = 1;k[0] = 0;
    for(i = 1;i <= n-1;i ++)
    {
        max = 0;t = i;
        for(j = 0;j <= i-1;j ++)
        {
            if(p[i].x < p[j].x&&p[i].y > p[j].y)
            {
                if(o[j] > max)
                {
                    max = o[j];
                    t = j;
                }
            }
        }
        o[i] = max+1;
        k[i] = t;
    }
    max = 0;t = 0;
    for(i = 0;i <= n-1;i ++)
    {
        if(max < o[i])
        {
            max = o[i];
            t = i;
        }
    }
    printf("%d\n",max);
    for(i = 1;i <= max;i ++)
    {
        q[i] = p[t].num+1;
        t = k[t];
    }
    for(i = max;i >= 1;i --)
    {
        if(i == max)
        printf("%d",q[i]);
        else
        printf(" %d",q[i]);
    }
    printf("\n");
    return 0;
}