首先,这是一道坑题,我拍了几百组数据都是对的,交上去就WA,原因下面会讲。。。

一开始我觉得要链剖,后来ZYH说。。。只要dfs序就可以解题。

然后,解法嘛。。。就是每个点到根的链都建成一棵线段树,然后发现会MLE,于是就可持久化了所有线段树。

在查询的时候呢,先找出两个点a, b的LCA,不妨叫c,然后找c的父亲叫d,每次比较k和seg[a] + seg[b] - seg[c] - seg[d]的大小就可以了。

 

  1 /**************************************************************
  2     Problem: 2588
  3     User: rausen
  4     Language: C++
  5     Result: Accepted
  6     Time:4396 ms
  7     Memory:51788 kb
  8 ****************************************************************/
  9  
 10 #include <cstdio>
 11 #include <cstdlib>
 12 #include <cstring>
 13 #include <algorithm>
 14  
 15 using namespace std;
 16  
 17 struct tree_node{
 18     int pos, dep, v, fa[20];
 19 } tr[150000];
 20  
 21 struct edges{
 22     int next, to;
 23 }e[250000];
 24  
 25 struct segment{
 26     int lson, rson, sum;
 27 } seg[2500000];
 28  
 29 int n, m, tot, TOT, cnt, sz, ans;
 30 int X, Y, Z, K;
 31 int first[150000], V[150000], N[150000], root[150000], num[150000];
 32  
 33 void add_edge(int x, int y){
 34     e[++TOT].next = first[x];
 35     first[x] = TOT;
 36     e[TOT].to = y;
 37 }
 38  
 39 void add_Edges(int x, int y){
 40     add_edge(x, y);
 41     add_edge(y, x);
 42 }
 43  
 44 int find(int x){
 45     int l = 1, r = tot;
 46     while (l < r){
 47         int mid = (l + r) >> 1;
 48         if (N[mid] < x) l = mid + 1;
 49         else r = mid;
 50     }
 51     return l;
 52 }
 53  
 54 void dfs(int p){
 55     num[++cnt] = p, tr[p].pos = cnt;
 56     int x, y;
 57     for (x = 1; x <= 16; ++x)
 58         if ((1 << x) < tr[p].dep) 
 59             tr[p].fa[x] = tr[tr[p].fa[x - 1]].fa[x - 1];
 60         else break;
 61     for (x = first[p]; x; x = e[x].next){
 62         y = e[x].to;
 63         if (tr[p].fa[0] != y){
 64             tr[y].fa[0] = p, tr[y].dep = tr[p].dep + 1;
 65             dfs(y);
 66         }
 67     }
 68 }
 69  
 70 void add(int l, int r, int x, int &y, int num){
 71     y = ++sz, seg[y].sum = seg[x].sum + 1;
 72     seg[y].lson = seg[x].lson, seg[y].rson = seg[x].rson;
 73     if (l == r) return;
 74     int mid = (l + r) >> 1;
 75     if (num <= mid)
 76         add(l, mid, seg[x].lson, seg[y].lson, num);
 77     else add(mid + 1, r, seg[x].rson, seg[y].rson, num);
 78 }
 79  
 80 int LCA(int x, int y){
 81     if (tr[x].dep < tr[y].dep) swap(x, y);
 82     int tmp = tr[x].dep - tr[y].dep;
 83     for (int i = 0; i <= 16; ++i)
 84         if (tmp & (1 << i)) x = tr[x].fa[i];
 85     for (int i = 16; i >= 0; --i)
 86         if (tr[x].fa[i] != tr[y].fa[i])
 87             x = tr[x].fa[i], y = tr[y].fa[i];
 88     if (x == y) return x;
 89     else return tr[x].fa[0];
 90 }
 91  
 92 int query(int x, int y, int K){
 93     int a = x, b = y, c = LCA(x, y), d = tr[c].fa[0];
 94     a = root[tr[a].pos], b = root[tr[b].pos], c = root[tr[c].pos], d = root[tr[d].pos];
 95     int l = 1, r = tot;
 96     while (l < r){
 97         int mid = (l + r) >> 1;
 98         int tmp = seg[seg[a].lson].sum + seg[seg[b].lson].sum - seg[seg[c].lson].sum - seg[seg[d].lson].sum;
 99         if (tmp >= K)
100             r = mid, a = seg[a].lson, b = seg[b].lson, c = seg[c].lson, d = seg[d].lson;
101         else
102             K -= tmp, l = mid + 1, a = seg[a].rson, b = seg[b].rson, c = seg[c].rson, d = seg[d].rson;
103     }
104     return N[l];
105 }
106  
107 int main(){
108     scanf("%d%d", &n, &m);
109     for (int i = 1; i <= n; ++i){
110         scanf("%d", &tr[i].v);
111         V[i] = tr[i].v;
112     }
113     sort(V + 1, V + n + 1);
114     N[++tot] = V[1];
115     for (int i = 2; i <= n; ++i)
116         if (V[i] != V[i - 1])
117             N[++tot] = V[i];
118     for (int i = 1; i <= n; ++i)
119         tr[i].v = find(tr[i].v);
120     for (int i = 1; i < n; ++i){
121         scanf("%d%d", &X, &Y);
122         add_Edges(X, Y);
123     }
124     cnt = 0;
125     tr[1].fa[0] = 0, tr[1].dep = 1;
126     dfs(1);
127      
128     root[0] = 0, seg[0].sum = seg[0].lson = seg[0].rson = 0;
129     for (int i = 1; i <= n; ++i){
130         int t = num[i];
131         add(1, tot, root[tr[tr[t].fa[0]].pos], root[i], tr[t].v);
132     }
133     while (m--){
134         scanf("%d%d%d", &X, &Y, &K);
135         X ^= ans;
136         ans = query(X ,Y ,K);
137         printf("%d", ans);
138         if (m) printf("\n");
139     }
140     return 0;
141 }
View Code

 (WA的原因:太坑爹了,我把根的深度设成0,然后倍增乱搞的时候RE了。。。)

posted on 2014-10-04 16:36  Xs酱~  阅读(1026)  评论(0编辑  收藏  举报