Minimal coverage -uva 覆盖线段，贪心

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define MAX_SIZE 100000 + 10
#define BOTTOM -50000 - 10
struct Points
{
    int x,y;
}a[MAX_SIZE],b[MAX_SIZE];
int cmp(const void *a,const void *b)
{
    struct Points * c=(Points*)a;
    struct Points * d=(Points*)b;
    if(c->x!=d->x)
    return c->x - d->x;/*升序*/
    else
    return c->y - d->y;
}
int main()
{
    int M,N,m,n,i,j,cases,t,p,q,min,max;
    scanf("%d",&N);
    for(cases=1;cases<=N;cases++)
    {
        int ok=0,k;
        scanf("%d",&M);
        for(i=0,j=0;scanf("%d%d",&m,&n);)
        {
            if(!m&&!n) break;
            if(m<M&&n>0) /*不在范围内的直接舍去*/
            {
                a[j].x=m;
                a[j].y=n;
                j++;
            }
        }
       qsort(a,j,sizeof(a[0]),cmp);
       if(a[0].x>0||j==0) {printf("0\n");continue;}
       for(i=0,t=0,q=0,max=BOTTOM;i<j;i++)
       {
           if(a[i].x<=t)
           {
               m=a[i].y-t;/*有效长度*/
               if(m>max)
               {
                   max=m;
                   p=i;/*储存坐标*/
               }
           }
           if(a[i+1].x>t||i==j-1)/*如果下一个坐标大于*/
           {
               /*就对上面所计算的区间进行取长*/
               b[q].x=a[p].x;
               b[q].y=a[p].y;
               q++;
               t=a[p].y;
               max=BOTTOM;
           }
           if(t>=M) break;
       }
       if(t>=M) ok=1;
       /*for(i=0;i<q;i++)
            printf("%d %d\n",b[i].x,b[i].y);*/
       if(ok)
       {
            printf("%d\n",q);
            for(i=0;i<q;i++)
            printf("%d %d\n",b[i].x,b[i].y);
       }
        else
        printf("0\n");

        if(cases<N)
        printf("\n");
        memset(a,0,sizeof(a));
        memset(b,0,sizeof(b));
    }
    return 0;
}