BZOJ3166 [Heoi2013]Alo

 1 /**************************************************************
 2     Problem: 3166
 3     User: rausen
 4     Language: C++
 5     Result: Accepted
 6     Time:1112 ms
 7     Memory:22964 kb
 8 ****************************************************************/
 9  
10 #include <cstdio>
11 #include <algorithm>
12 #include <set>
13  
14 using namespace std;
15 const int N = 50005;
16 const int inf = 1e9;
17 struct data {
18     int v, w;
19     data() {}
20     data(int _v, int _w) : v(_v), w(_w) {}
21      
22     inline bool operator < (const data &x) const {
23         return v > x.v;
24     }
25 } a[N];
26  
27 struct trie_node {
28     int son[2], cnt;
29 } t[N * 35];
30 int cnt_trie;
31  
32 int n, root[N];
33 set <int> q;
34  
35 inline int read() {
36     int x = 0;
37     char ch = getchar();
38     while (ch < ‘0‘ || ‘9‘ < ch)
39         ch = getchar();
40     while (‘0‘ <= ch && ch <= ‘9‘) {
41         x = x * 10 + ch - ‘0‘;
42         ch = getchar();
43     }
44     return x;
45 }
46  
47 int A[35];
48 void insert(int &root, int v) {
49     int R = root, now = ++cnt_trie, i;
50     root = now;
51     for (i = 0; i <= 30; ++i)
52         A[i] = v & 1, v >>= 1;
53     reverse(A, A + 31);
54     for (i = 0; i <= 30; ++i) {
55         t[now].son[0] = t[R].son[0], t[now].son[1] = t[R].son[1];
56         R = t[R].son[A[i]], now = t[now].son[A[i]] = ++cnt_trie;
57         t[now].cnt = t[R].cnt + 1;
58     }
59 }
60  
61 int query(int x, int y, int v) {
62     int res = 0, i;
63     for (i = 0; i <= 30; ++i)
64         A[i] = v & 1, v >>= 1;
65     reverse(A, A + 31);
66     for (i = 0; i <= 30; ++i) {
67         if (t[y].son[!A[i]] - t[x].son[!A[i]])
68             x = t[x].son[!A[i]], y = t[y].son[!A[i]], res += (1 << 30 - i);
69             else x = t[x].son[A[i]], y = t[y].son[A[i]];
70     }
71     return res;
72 }
73  
74 int main() {
75     int i, l, r, ans = 0;
76     n = read(), root[0] = cnt_trie = 1;
77     for (i = 1; i <= n; ++i) {
78         a[i] = data(read(), i), root[i] = root[i - 1];
79         insert(root[i], a[i].v);
80     }
81     sort(a + 1, a + n + 1);
82     q.insert(-1), q.insert(-2), q.insert(inf), q.insert(inf + 1);
83     q.insert(a[i].w);
84     for (i = 2; i <= n; ++i) {
85         l = max(1, *--(--q.lower_bound(a[i].w)) + 1);
86         r = min(n, *++q.upper_bound(a[i].w) - 1);
87         if (l > r) continue;
88         ans = max(ans, query(root[l - 1], root[r], a[i].v));
89         q.insert(a[i].w);
90     }
91     printf("%d\n", ans);
92     return 0;
93 }