【SPOJ】2798 Query on a tree again!

  1 #include<cstdio>

  2 #include<cstring>

  3 #include<iostream>

  4 #include<queue>

  5 #define MAXN 100100

  6 #define MAXM 200100

  7 using namespace std;

  8 bool vis[MAXN];

  9 int e, first[MAXN], next[MAXM], v[MAXM];

 10 struct LCT {

 11     int bef[MAXN];

 12     int next[MAXN][2], pre[MAXN], key[MAXN], sum[MAXN];

 13     void Init() {

 14         memset(next, 0, sizeof(next));

 15         memset(pre, 0, sizeof(pre));

 16         memset(key, 0, sizeof(key));

 17         memset(sum, 0, sizeof(sum));

 18     }

 19     inline void PushUp(int x) {

 20         sum[x] = key[x] + sum[next[x][0]] + sum[next[x][1]];

 21     }

 22     inline void Rotate(int x, int kind) {

 23         int y, z;

 24         y = pre[x];

 25         z = pre[y];

 26         next[y][!kind] = next[x][kind];

 27         pre[next[x][kind]] = y;

 28         next[z][next[z][1] == y] = x;

 29         pre[x] = z;

 30         next[x][kind] = y;

 31         pre[y] = x;

 32         PushUp(y);

 33     }

 34     void Splay(int x) {

 35         int rt;

 36         for (rt = x; pre[rt]; rt = pre[rt])

 37             ;

 38         if (x != rt) {

 39             bef[x] = bef[rt];

 40             bef[rt] = 0;

 41             while (pre[x]) {

 42                 if (next[pre[x]][0] == x)

 43                     Rotate(x, 1);

 44                 else

 45                     Rotate(x, 0);

 46             }

 47             PushUp(x);

 48         }

 49     }

 50     void Access(int x) {

 51         int father;

 52         for (father = 0; x; x = bef[x]) {

 53             Splay(x);

 54             pre[next[x][1]] = 0;

 55             bef[next[x][1]] = x;

 56             next[x][1] = father;

 57             pre[father] = x;

 58             bef[father] = 0;

 59             father = x;

 60             PushUp(x);

 61         }

 62     }

 63     int Select(int x, int k) {

 64         while (!(sum[next[x][0]] + key[x] == k && key[x])) {

 65             if (sum[next[x][0]] + key[x] >= k)

 66                 x = next[x][0];

 67             else

 68                 x = next[x][1];

 69         }

 70         return x;

 71     }

 72     int Query(int x) {

 73         Access(x);

 74         Splay(1);

 75         if (sum[1])

 76             return Select(1, 1);

 77         return -1;

 78     }

 79     void Change(int x) {

 80         key[x] ^= 1;

 81         Splay(x);

 82     }

 83 } lct;

 84 int INT() {

 85     char ch;

 86     int res;

 87     while (ch = getchar(), !isdigit(ch))

 88         ;

 89     for (res = ch - '0'; ch = getchar(), isdigit(ch);)

 90         res = res * 10 + ch - '0';

 91     return res;

 92 }

 93 inline void AddEdge(int x, int y) {

 94     v[e] = y;

 95     next[e] = first[x];

 96     first[x] = e++;

 97 }

 98 void BFS(int x) {

 99     int i, y;

100     queue<int> q;

101     vis[x] = true;

102     q.push(x);

103     while (!q.empty()) {

104         x = q.front();

105         q.pop();

106         for (i = first[x]; i != -1; i = next[i]) {

107             y = v[i];

108             if (!vis[y]) {

109                 lct.bef[y] = x;

110                 vis[y] = true;

111                 q.push(y);

112             }

113         }

114     }

115 }

116 int main() {

117     int n, q, i, x, y;

118     while (~scanf("%d%d", &n, &q)) {

119         lct.Init();

120         memset(vis, false, sizeof(vis));

121         memset(first, -1, sizeof(first));

122         for (e = 0, i = 1; i < n; i++) {

123             x = INT(), y = INT();

124             AddEdge(x, y);

125             AddEdge(y, x);

126         }

127         BFS(1);

128         while (q--) {

129             x = INT(), y = INT();

130             if (x)

131                 printf("%d\n", lct.Query(y));

132             else

133                 lct.Change(y);

134         }

135     }

136     return 0;

137 }