Aizu 2677 Breadth-First Search by Foxpower(LCA + BFS)

题目链接

题目大致意思就是给出含有n节点的树，1为树根。从1开始bfs搜索整棵树，不过有顺序。深度小的比大的优先，
同一深度的其优先值为其父节点在上一层的搜索顺序，如果同属一个父节点，那么就是节点编号小的优先。然后求出路径总和sum。比如这次搜索到了u，下次需要搜索到v，
那么sum += dis(u, v)。树上的dis就是lca了，因为边权为1.
然后剩下的就是模拟这个过程求解了。

/*****************************************Author      :Crazy_AC(JamesQi)Time        :2016File Name   :*****************************************/// #pragma comment(linker, "/STACK:1024000000,1024000000")#include <iostream>#include <algorithm>#include <iomanip>#include <sstream>#include <string>#include <stack>#include <queue>#include <deque>#include <vector>#include <map>#include <set>#include <cstdio>#include <cstring>#include <cmath>#include <cstdlib>#include <climits>using namespace std;#define MEM(x,y) memset(x, y,sizeof x)#define pk push_back#define lson rt << 1#define rson rt << 1 | 1#define bug cout << "BUG HERE\n"#define debug(x) cout << #x << " = " << x << endl#define ALL(v) (v).begin(), (v).end()#define lowbit(x) ((x)&(-x))#define Unique(x) sort(ALL(x)); (x).resize(unique(ALL(x)) - (x).begin())#define BitOne(x) __builtin_popcount(x)#define showtime printf("time = %.15f\n",clock() / (double)CLOCKS_PER_SEC)#define Rep(i, l, r) for (int i = l;i <= r;++i)#define Rrep(i, r, l) for (int i = r;i >= l;--i)typedef long long LL;typedef unsigned long long ULL;const int maxn = 1e5 + 123;const int LOGN = 20;int head[maxn], nxt[maxn*2], pnt[maxn*2], ecnt;inline void addedge(int u,int v) {    pnt[ecnt] = v, nxt[ecnt] = head[u], head[u] = ecnt++;    pnt[ecnt] = u, nxt[ecnt] = head[v], head[v] = ecnt++;}// vector<vector<int> > G;int n;int fa[maxn];struct node {    int pre, u;    //pre为其父节点的优先值,pre相同时就是u小的优先    //同一层访问的优先顺序    bool operator < (const node& rhs) const {        return pre < rhs.pre || (pre == rhs.pre && u < rhs.u);    }};struct _LCA {    int dep[maxn];    int fa[LOGN][maxn];    void dfs(int u,int pre, int depth) {        fa[0][u] = pre;dep[u] = depth;        for (int i = head[u];~i;i = nxt[i]) {            if (pnt[i] == pre) continue;            dfs(pnt[i], u, depth + 1);        }    }    inline void Build(int n) {        for (int k = 0;k < LOGN - 1;++k) {            for (int u = 1;u <= n;++u) {                if (fa[k][u] == -1) fa[k + 1][u] = -1;                else fa[k + 1][u] = fa[k][ fa[k][u] ];            }        }    }    inline int upslope(int u,int p) {        for (int k = 0;k < LOGN - 1;++k)            if ((p>>k) & 1) u = fa[k][u];        return u;    }    inline int LCA(int u,int v) {        if (dep[u] < dep[v]) swap(u, v);        u = upslope(u, dep[u] - dep[v]);        if (u == v) return u;        for (int k = LOGN - 1;k >= 0;--k) {            if (fa[k][u] != fa[k][v])                 u = fa[k][u], v = fa[k][v];        }        return fa[0][u];    }    LL get_dis(int u, int v) {        int lca = LCA(u, v);        return (LL)dep[u] + (LL)dep[v] - 2LL * (LL)dep[lca];    }}lca;inline void bfs_init() {    LL sum = 0;    vector<node> vec;    for (int i = head[1];~i;i = nxt[i]) {        int v = pnt[i];        vec.push_back(node{1, v});    }    int last = 1;//上一层访问的最后一个点的编号    while(!vec.empty()) {        vec.push_back(node{-1, last});        sort(ALL(vec));        int size = vec.size();        for (int i = 1;i < size;++i) {            sum += (LL)lca.get_dis(vec[i].u, vec[i - 1].u);        }        vector<node> temp;        Rep(i, 1, size - 1) {            int u = vec[i].u;            for (int j = head[u];~j;j = nxt[j]) {                int v = pnt[j];                if (v == fa[u]) continue;                temp.push_back(node{i + 1, v});            }        }        last = vec.back().u;        vec.clear();        vec = temp;    }    cout << sum << endl;}int main(int argc, const char * argv[]){        // freopen("in.txt","r",stdin);    // freopen("out.txt","w",stdout);    // ios::sync_with_stdio(false);    // cout.sync_with_stdio(false);    // cin.sync_with_stdio(false);    while(~scanf("%d", &n)) {        // G.clear();        // G.resize(n + 2);        memset(head, -1, sizeof head), ecnt = 0;        Rep(i, 2, n) {            scanf("%d", &fa[i]);            addedge(i, fa[i]);        }        lca.dfs(1, -1, 0);        lca.Build(n);        bfs_init();    }    // showtime;    return 0;}