[hdu4123]dfs区间化+RMQ

题意：给一个树编号0~n-1，一个数组a[i]为节点i在树上走的最大距离（不重复点），然后求最大的区间，使得区间最大差异小于某个值。dfs求出每个数组，同时区间化。枚举区间左边界，右边界同样递增，类似单调队列，区间最值用RMQ查询（常数小）。

  1 #pragma comment(linker, "/STACK:10240000,10240000")

  2 

  3 #include <iostream>

  4 #include <cstdio>

  5 #include <algorithm>

  6 #include <cstdlib>

  7 #include <cstring>

  8 #include <map>

  9 #include <queue>

 10 #include <deque>

 11 #include <cmath>

 12 #include <vector>

 13 #include <ctime>

 14 #include <cctype>

 15 #include <set>

 16 

 17 using namespace std;

 18 

 19 #define mem0(a) memset(a, 0, sizeof(a))

 20 #define lson l, m, rt << 1

 21 #define rson m + 1, r, rt << 1 | 1

 22 #define define_m int m = (l + r) >> 1

 23 #define Rep(a, b) for(int a = 0; a < b; a++)

 24 #define lowbit(x) ((x) & (-(x)))

 25 #define constructInt4(name, a, b, c, d) name(int a = 0, int b = 0, int c = 0, int d = 0): a(a), b(b), c(c), d(d) {}

 26 #define constructInt3(name, a, b, c) name(int a = 0, int b = 0, int c = 0): a(a), b(b), c(c) {}

 27 #define constructInt2(name, a, b) name(int a = 0, int b = 0): a(a), b(b) {}

 28 

 29 typedef double db;

 30 typedef long long LL;

 31 typedef pair<int, int> pii;

 32 typedef multiset<int> msi;

 33 typedef multiset<int>::iterator msii;

 34 typedef set<int> si;

 35 typedef set<int>::iterator sii;

 36 typedef vector<int> vi;

 37 

 38 const int dx[8] = {1, 0, -1, 0, 1, 1, -1, -1};

 39 const int dy[8] = {0, -1, 0, 1, -1, 1, 1, -1};

 40 const int maxn = 1e5 + 7;

 41 const int maxm = 1e5 + 7;

 42 const int maxv = 1e7 + 7;

 43 const int MD = 1e9 +7;

 44 const int INF = 1e9 + 7;

 45 const double PI = acos(-1.0);

 46 const double eps = 1e-10;

 47 

 48 template<class T> struct MonotoneQueue{

 49     deque<T> Q;

 50     MonotoneQueue<T>() { Q.clear(); }

 51     void clear() { Q.clear(); }

 52     bool empty() { return Q.empty(); }

 53     void add_back(T x) { while (!Q.empty() && !(Q.back() < x)) Q.pop_back(); Q.push_back(x); }

 54     void pop_front() { Q.pop_front(); }

 55     T back2() { if(Q.size() < 2) return T(); return *(Q.end() - 2); }

 56     T front() { return Q.front(); }

 57 };

 58 

 59 template<class edge> struct Graph {

 60     vector<vector<edge> > adj;

 61     Graph(int n) { adj.clear(); adj.resize(n + 5); }

 62     Graph() { adj.clear(); }

 63     void resize(int n) { adj.resize(n + 5); }

 64     void add(int s, edge e){ adj[s].push_back(e); }

 65     void del(int s, edge e) { adj[s].erase(find(iter(adj[s]), e)); }

 66     void clear() { adj.clear(); }

 67     vector<edge>& operator [](int t) { return adj[t]; }

 68 };

 69 

 70 Graph<int> G, W;

 71 

 72 

 73 

 74 int maxd, id, d, n, m;

 75 int dis[maxn], t[maxn], maxf[maxn][20], minf[maxn][20];

 76 bool vis[maxn];

 77 

 78 void DFS(int node) {

 79     vis[node] = true;

 80     dis[node] = max(dis[node], d);

 81     if (d > maxd) {

 82         maxd = d;

 83         id = node;

 84     }

 85     for (int i = 0; i < G[node].size(); i++) {

 86         int u = G[node][i];

 87         if (!vis[u]) {

 88             d += W[node][i];

 89             DFS(u);

 90             d -= W[node][i];

 91         }

 92     }

 93 }

 94 

 95 void InitRMQ() {

 96     for (int i = 1; i <= n; i++) maxf[i][0] = minf[i][0] = dis[i];

 97     for (int j = 1; (1 << j) <= n; j++) {

 98         for (int i = 1; i + (1 << j) - 1 <= n; i++) {

 99             maxf[i][j] = max(maxf[i][j - 1], maxf[i + (1 << (j - 1))][j - 1]);

100             minf[i][j] = min(minf[i][j - 1], minf[i + (1 << (j - 1))][j - 1]);

101         }

102     }

103 }

104 int RMQ_max(int L, int R) {

105     int x = t[R - L + 1];

106     return max(maxf[L][x], maxf[R - (1 << x) + 1][x]);

107 }

108 int RMQ_min(int L, int R) {

109     int x = t[R - L + 1];

110     return min(minf[L][x], minf[R - (1 << x) + 1][x]);

111 }

112 

113 int solve(int q) {

114     int L = 1, ans = 0;

115     for (int R = 1; R <= n; R++) {

116         while (RMQ_max(L, R) - RMQ_min(L, R) > q) L++;

117         ans = max(ans, R - L + 1);

118     }

119     return ans;

120 }

121 

122 int main() {

123     //freopen("in.txt", "r", stdin);

124     for (int i = 1; i <= 50000; i++) {

125         int j = 0;

126         while ((1 << (j + 1)) <= i) j++;

127         t[i] = j;

128     }

129     while (cin >> n >> m, n || m) {

130         G.clear(); G.resize(n);

131         W.clear(); W.resize(n);

132         for (int i = 1, u, v, w; i < n; i++) {

133             scanf("%d%d%d", &u, &v, &w);

134             G.add(u, v);

135             W.add(u, w);

136             G.add(v, u);

137             W.add(v, w);

138         }

139         mem0(vis);

140         maxd = -1;

141         DFS(1);

142         int node1 = id;

143         mem0(vis);

144         maxd = -1;

145         DFS(id);

146         int node2 = id;

147         mem0(dis);

148         mem0(vis);

149         DFS(node1);

150         mem0(vis);

151         DFS(node2);

152         InitRMQ();

153         for (int i = 0, q; i < m; i++) {

154             scanf("%d", &q);

155             printf("%d\n", solve(q));

156         }

157     }

158     return 0;

159 }

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