HDU 4004 The Frog's Games(二分)

题意理解的有些问题。
 1 #include <iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<algorithm>
 5 using namespace std;
 6 #define LL __int64
 7 LL p[501001];
 8 int n;
 9 int judge(int x,int m)
10 {
11     int pre = 0,num = 0,i;
12     for(i = 0;i <= n;i ++)
13     {
14         if(p[i] - pre <= x)
15         ;
16         else
17         {
18             num ++;
19             pre = p[i-1];
20         }
21     }
22     if(num + 1 > m)
23     return 0;
24     else
25     return 1;
26 }
27 int main()
28 {
29     int m,i,l;
30     LL str,mid,end,minz;
31     while(scanf("%d%d%d",&l,&n,&m)!=EOF)
32     {
33         for(i = 0; i < n; i ++)
34             scanf("%I64d",&p[i]);
35         sort(p,p+n);
36         if(n == 0||m == 1)
37         {
38             printf("%d
",l);
39             continue;
40         }
41         p[n] = l;
42         minz = p[0];
43         for(i = 0;i < n;i ++)
44         {
45             minz = max(minz,p[i+1]-p[i]);
46         }
47         str = minz;end = l;
48         while(str < end)
49         {
50             mid = (str+end)/2;
51             if(judge(mid,m) == 0)
52             str = mid + 1;
53             else
54             end = mid;
55         }
56         printf("%I64d
",str);
57     }
58     return 0;
59 }