BZOJ 3747: [POI2015]Kinoman
考虑枚举起点，找一个最远的右端点使得以这个点为起点的答案最大
用线段树维护，需要设计一种标记，使得含有多个数的前缀中减去这个数的贡献
考虑这样设计，对于第一次出现的数，对其赋值$w[i]$
第二次出现 赋值$-w[i]$
第三次出现 赋值为0
这样前缀和就满足多次出现的数不会计算贡献
再维护前驱节点和后驱节点，每次删去开头的数，维护一下后驱节点
1 #include <bits/stdc++.h> 2 using namespace std; 3 4 #define ll long long 5 #define N 1000010 6 #define INF 0x3f3f3f3f3f3f3f3f 7 int n, m, f[N], pre[N], nx[N]; 8 ll w[N], v[N]; 9 map <int, int> mp; 10 11 namespace SEG 12 { 13 ll Max[N << 2], lazy[N << 2]; 14 void init() 15 { 16 memset(Max, 0, sizeof Max); 17 memset(lazy, 0, sizeof lazy); 18 } 19 void pushdown(int id) 20 { 21 if (!lazy[id]) return; 22 lazy[id << 1] += lazy[id]; 23 Max[id << 1] += lazy[id]; 24 lazy[id << 1 | 1] += lazy[id]; 25 Max[id << 1 | 1] += lazy[id]; 26 lazy[id] = 0; 27 } 28 void update(int id, int l, int r, int ql, int qr, ll val) 29 { 30 if (l >= ql && r <= qr) 31 { 32 lazy[id] += val; 33 Max[id] += val; 34 return; 35 } 36 pushdown(id); 37 int mid = (l + r) >> 1; 38 if (ql <= mid) update(id << 1, l, mid, ql, qr, val); 39 if (qr > mid) update(id << 1 | 1, mid + 1, r, ql, qr, val); 40 Max[id] = max(Max[id << 1], Max[id << 1 | 1]); 41 } 42 } 43 44 int main() 45 { 46 while (scanf("%d%d", &n, &m) != EOF) 47 { 48 for (int i = 1; i <= n; ++i) scanf("%d", f + i); 49 for (int i = 1; i <= m; ++i) scanf("%lld", w + i); 50 mp.clear(); 51 for (int i = 1; i <= n; ++i) 52 { 53 if (mp.find(f[i]) != mp.end()) 54 pre[i] = mp[f[i]]; 55 else 56 pre[i] = 0; 57 mp[f[i]] = i; 58 } 59 mp.clear(); 60 for (int i = n; i >= 1; --i) 61 { 62 if (mp.find(f[i]) != mp.end()) 63 nx[i] = mp[f[i]]; 64 else 65 nx[i] = n + 1; 66 mp[f[i]] = i; 67 } 68 for (int i = 1; i <= n; ++i) 69 { 70 if (pre[i] == 0) v[i] = w[f[i]]; 71 else if (v[pre[i]] == w[f[pre[i]]]) v[i] = -w[f[i]]; 72 else v[i] = 0; 73 } 74 SEG::init(); 75 for (int i = 1; i <= n; ++i) 76 SEG::update(1, 1, n, i, n, v[i]); 77 ll res = 0; 78 for (int i = 1; i <= n; ++i) 79 { 80 res = max(res, SEG::Max[1]); 81 SEG::update(1, 1, n, i, n, -v[i]); 82 if (nx[i] != n + 1) 83 { 84 SEG::update(1, 1, n, nx[i], n, -v[nx[i]]); 85 v[nx[i]] = w[f[nx[i]]]; 86 SEG::update(1, 1, n, nx[i], n, v[nx[i]]); 87 if (nx[nx[i]] != n + 1) 88 { 89 v[nx[nx[i]]] = -v[nx[i]]; 90 SEG::update(1, 1, n, nx[nx[i]], n, -v[nx[i]]); 91 } 92 } 93 } 94 printf("%lld\n", res); 95 } 96 return 0; 97 }
