HDU 6203 ping Ping ping [LCA, greedy, DFS sequence, BIT (tree-like array)]

Topic Link: "http://acm.hdu.edu.cn/showproblem.php?pid=6203"

Test instructions: Give a tree, if (A, B) the path has a bad point, then (A, B) is not connected, give some of the wrong point pair, and then determine the minimum number of bad points.

The following: The LCA of each point pair is then sorted according to the depth of the LCA. Starting with the deepest point pair of the LCA, if a or B point is already a bit marked, then continue, no, the sub-tree of the LCA (b) is added 1 per vertex.

#include <bits/stdc++.h>using namespace Std;const int maxn = 2e5 + 5;int N, Q;int C[MAXN], IN[MAXN], OUT[MAXN], cnt;s    truct edge{int id, next; Edge (int id = 0, int next = 0): ID (ID), next (next) {}} E[MAXN << 1];    bidirectional Edge int HEAD[MAXN], tot;void Initedge () {memset (c, 0, sizeof (c));    CNT = 0;    for (int i = 0; I <= N; i++) head[i] = 1; tot = 0;}    void Addedge (int u, int v) {E[tot] = Edge (V, Head[u]); Head[u] = tot++;}    int SIZ[MAXN], TOP[MAXN], DEP[MAXN], Fa[maxn];int clk;//requires initialization of void DFS1 (int u, int p) {In[u] = ++cnt;    Dep[u] = dep[p] + 1;    Fa[u] = p, siz[u] = 1;        for (int k = Head[u]; K! =-1; k = e[k].next) {int id = e[k].id;        if (id = = p) continue;        DFS1 (ID, u);    Siz[u] + = Siz[id]; } Out[u] = cnt;}    void DFS2 (int u, int p) {int son =-1;        for (int k = Head[u]; K! =-1; k = e[k].next)//Find heavy son {int id = e[k].id;        if (id = = p) continue;    if (son = =-1 | | siz[id] > Siz[son]) son = ID; } if (sOn! =-1) {Top[son] = Top[u];    DFS2 (son, u);        } for (int k = Head[u]; K! =-1; k = e[k].next) {int id = e[k].id;        if (id = = P | | id = = son) continue;        TOP[ID] = ID;    DFS2 (ID, u);        }}int LCA (int x, int y) {while (top[x]! = Top[y]) {if (Dep[top[x]] < Dep[top[y]]) swap (x, y);    x = fa[top[x]];    } if (Dep[x] > Dep[y]) swap (x, y); return x;}    struct node{int u, V, LCA;    BOOL operator < (const node &t) const {return DEP[LCA] > DEP[T.LCA]; }} qry[50050];int low_bit (int x) {return x & x;}        void update (int x, int val) {while (x <= N) {c[x] + = val;    x + = Low_bit (x);    }}int get_sum (int x) {int ret = 0;        while (x > 0) {ret + = c[x];    X-= Low_bit (x); } return ret;}        int main () {while (~SCANF ("%d", &n)) {n++;        Initedge ();            for (int i = 1; I <= N-1; i++) {int u, v; scanf ("%d%d ", &u, &v);            u++, v++;        Addedge (U, v), Addedge (V, u);        } DFS1 (1, 0), top[1] = 1,DFS2 (1, 0);        scanf ("%d", &q);            for (int i = 1; I <= Q; i++) {scanf ("%d%d", &qry[i].u, &AMP;QRY[I].V);            qry[i].u++, qry[i].v++;        QRY[I].LCA = LCA (qry[i].u, QRY[I].V);        } sort (qry + 1, qry + 1 + Q);        int ans = 0;            for (int i = 1; I <= Q; i++) {int u = QRY[I].LCA;            int ret = Get_sum (in[qry[i].u]) + get_sum (IN[QRY[I].V]);            if (ret) continue;            ans++;            Update (In[u], 1);        Update (Out[u] + 1,-1);    } printf ("%d\n", ans); } return 0;}

　　

HDU 6203 ping Ping ping [LCA, greedy, DFS sequence, BIT (tree-like array)]