[HDOJ6119] 小小粉丝度度熊（尺取）

 1 /*
 2 ━━━━━┒ギリギリ♂ eye！
 3 ┓┏┓┏┓┃キリキリ♂ mind！
 4 ┛┗┛┗┛┃＼○／
 5 ┓┏┓┏┓┃ /
 6 ┛┗┛┗┛┃ノ)
 7 ┓┏┓┏┓┃
 8 ┛┗┛┗┛┃
 9 ┓┏┓┏┓┃
10 ┛┗┛┗┛┃
11 ┓┏┓┏┓┃
12 ┛┗┛┗┛┃
13 ┓┏┓┏┓┃
14 ┃┃┃┃┃┃
15 ┻┻┻┻┻┻
16 */
17 #include <bits/stdc++.h>
18 using namespace std;
19 #define fr first
20 #define sc second
21 #define cl clear
22 #define BUG puts("here!!!")
23 #define W(a) while(a--)
24 #define pb(a) push_back(a)
25 #define Rint(a) scanf("%d", &a)
26 #define Rll(a) scanf("%I64d", &a)
27 #define Rs(a) scanf("%s", a)
28 #define Cin(a) cin >> a
29 #define FRead() freopen("in", "r", stdin)
30 #define FWrite() freopen("out", "w", stdout)
31 #define Rep(i, len) for(int i = 0; i < (len); i++)
32 #define For(i, a, len) for(int i = (a); i < (len); i++)
33 #define Cls(a) memset((a), 0, sizeof(a))
34 #define Clr(a, x) memset((a), (x), sizeof(a))
35 #define Full(a) memset((a), 0x7f7f7f, sizeof(a))
36 #define lrt rt << 1
37 #define rrt rt << 1 | 1
38 #define pi 3.14159265359
39 #define RT return
40 #define lowbit(x) x & (-x)
41 #define onenum(x) __builtin_popcount(x)
42 typedef long long LL;
43 typedef long double LD;
44 typedef unsigned long long ULL;
45 typedef pair<int, int> pii;
46 typedef pair<string, int> psi;
47 typedef pair<LL, LL> pll;
48 typedef map<string, int> msi;
49 typedef vector<int> vi;
50 typedef vector<LL> vl;
51 typedef vector<vl> vvl;
52 typedef vector<bool> vb;
53 
54 const int maxn = 100100;
55 int n;
56 LL m;
57 pll seg[maxn];
58 
59 signed main() {
60     // freopen("in", "r", stdin);
61     while(~Rint(n)) {
62         Rll(m);
63         For(i, 1, n+1) {
64             Rll(seg[i].first);
65             Rll(seg[i].second);
66         }
67         sort(seg+1, seg+n+1);
68         int tn = n;
69         n = 0;
70         For(i, 1, tn+1) {
71             if(i != 1 && seg[i].first <= seg[n].second) {
72                 seg[n].second = max(seg[n].second, seg[i].second);
73             }
74             else seg[++n] = seg[i];
75         }
76         int lo = 1;
77         LL cur = 0, ret = 0;
78         For(i, 1, n+1) {
79             if(i != 1) {
80                 cur += seg[i].first - seg[i-1].second - 1;
81             }
82             while(i != 1 && cur > m) {
83                 cur -= seg[lo+1].first - seg[lo].second - 1;
84                 lo++;
85             }
86             ret = max(ret, seg[i].second - seg[lo].first + 1 + m - cur);
87         }
88         printf("%I64d\n", ret);
89     }
90     return 0;
91 }