BZOJ2157 旅行 模拟

题目内容：

Ray 乐忠于旅游，这次他来到了T 城。T 城是一个水上城市，一共有 N 个景点，有些景点之间会用一座桥连接。为了方便游客到达每个景点但又为了节约成本，T 城的任意两个景点之间有且只有一条路径。换句话说， T 城中只有N − 1 座桥。Ray 发现，有些桥上可以看到美丽的景色，让人心情愉悦，但有些桥狭窄泥泞，令人烦躁。于是，他给每座桥定义一个愉悦度w，也就是说，Ray 经过这座桥会增加w 的愉悦度，这或许是正的也可能是负的。有时，Ray 看待同一座桥的心情也会发生改变。现在，Ray 想让你帮他计算从u 景点到v 景点能获得的总愉悦度。有时，他还想知道某段路上最美丽的桥所提供的最大愉悦度，或是某段路上最糟糕的一座桥提供的最低愉悦度。

题目分析：

　　一道码农题，最难的地方在于如何判断输入的是哪个操作，所以要深刻掌握switch，下面我来讲讲switch的用法。

　　switch的主要结构是：

switch(a){
    case x:{......;break;}
    case y:{......;break;}
    default:{.......}      
}

值得注意的是case可以写任意多个且不能像if那样进行大于小于等的比较，所以switch的用处没有if大，而且switch可以完全用if代替，但是switch可以更方便地判断数字是否是这个并且作出操作。考虑到编程习惯，所以switch中case后面的括号是可以省略的。

题目代码：

　　

#include<bits/stdc++.h>
#define SUM t[now].sum
#define MIN t[now].minn
#define MAX t[now].maxx
using namespace std;
struct edge{
    int to,w;
};
const int INF = 120000;
const int maxn = 320000;
vector <edge> g[maxn];
int d[maxn],arr[maxn],fa[maxn],son[maxn],head[maxn],sz[maxn],num[maxn],dep[maxn];
int to_fa[maxn],fto_fa[maxn];
struct ed{int from,to;};
vector <ed> edges;
void dfs1(int now,int f,int d){
    arr[now] = 1;
    dep[now] = d;
    fa[now] = f;
    sz[now] = 1;
    int maxx = 0;
    for(int i=0;i<g[now].size();i++){
    if(arr[g[now][i].to]){
        to_fa[now] = i;
        continue;
    }
    fto_fa[g[now][i].to] = i;
    dfs1(g[now][i].to,now,d+1);
    sz[now] += sz[g[now][i].to];
    if(sz[g[now][i].to] > maxx){
        maxx = sz[g[now][i].to];
        son[now] = g[now][i].to;
    }
    }
}

int a[220000];
int bh = 0;

void dfs2(int now,int h){
    arr[now] = 1;
    head[now] = h;
    for(int i=0;i<g[now].size();i++){
    if(g[now][i].to == son[now]&&!arr[g[now][i].to]){
        num[now] = ++bh;
        a[bh] = g[now][i].w;
        dfs2(g[now][i].to,h);
        break;
    }
    }
    for(int i=0;i<g[now].size();i++){
    if(g[now][i].to != son[now] && arr[g[now][i].to]==0){
        dfs2(g[now][i].to,g[now][i].to);
    }
    }
}
struct node{
    int sum,minn,maxx;
    int f;
}t[1200000];
void push_down(int);
void push_up(int now){
    if(t[now].f)push_down(now);
    if(t[now * 2].f) push_down(now*2);
    if(t[now*2+1].f)push_down(now*2+1);
    SUM = t[now * 2].sum + t[now * 2 + 1].sum;
    MIN = min(t[now * 2].minn,t[now*2+1].minn);
    MAX = max(t[now*2].maxx,t[now*2+1].maxx);
}

void build_tree(int l,int r,int now){
    if(l == r){
    SUM = MAX = MIN  = a[l];
    return;
    }
    int mid = (l+r) >> 1;
    build_tree(l,mid,now * 2);
    build_tree(mid+1,r,now * 2 + 1);
    push_up(now);
}

void push_down(int now){
    SUM = -SUM;
    swap(MIN,MAX);
    MIN = -MIN;
    MAX = -MAX;
    t[now * 2].f ^= 1;
    t[now * 2 + 1].f ^=1;
    t[now].f = 0;
}

struct ask{
    int u,v,dir;
}A[120000];
int pre[120000];
struct point{
    int dis,num;
};
vector <point> lca[120000];
int get_l[120000];
int found(int x){
    int rx = x;
    while(pre[rx]!=rx)rx = pre[rx];
    while(pre[x]!=rx){
    int temp = pre[x];
    pre[x] = rx;
    x = temp;
    }
    return rx;
}
void tarjan(int now,int fa){
    arr[now] = 1;
    for(int i=0;i<lca[now].size();i++){
    if(arr[lca[now][i].dis]){
        get_l[lca[now][i].num] = found(lca[now][i].dis);
    }
    }
    for(int i=0;i<g[now].size();i++){
    if(arr[g[now][i].to]) continue;
    tarjan(g[now][i].to,now);
    }
    pre[found(now)] = found(fa);
}

void change(int l,int r,int c,int delta,int now){
    if(t[now].f) push_down(now);
    if(l == c && r == c){
    SUM = delta;
    MIN = delta;
    MAX = delta;
    return;
    }
    int mid = (l+r) >> 1;
    if(c <= mid)change(l,mid,c,delta,now * 2);
    else change(mid+1,r,c,delta,now * 2 + 1);
    push_up(now);
}
void opp(int l,int r,int begin,int end,int now){//[l,r]树,[begin,end]询问
    if(t[now].f) push_down(now);
    if(begin>r||end<l||begin>end)return;
    if(l>=begin&&r<=end){
    t[now].f ^=1;
    if(t[now].f)push_down(now);
    return;
    }
    int mid = (l + r) >> 1;
    opp(l,mid,begin,end,now*2);
    opp(mid+1,r,begin,end,now*2+1);
    push_up(now);
}

struct stru{int sum,max,min;};

stru merge(stru a,stru b){
    stru c = (stru){a.sum+b.sum,max(a.max,b.max),min(a.min,b.min)};
    return c;
}

stru get_sum(int l,int r,int begin,int end,int now){
    if(t[now].f) push_down(now);
    if(begin > r || end < l||begin>end) return (stru){0,-INT_MAX,INT_MAX};
    if(l >= begin && r <= end){
    return (stru){SUM,MAX,MIN};
    }
    int mid = (l+r) >> 1;
    stru ans = get_sum(l,mid,begin,end,now * 2);
    ans = merge(ans,get_sum(mid+1,r,begin,end,now*2+1));
    push_up(now);
    return ans;
}

int main(){
    ios::sync_with_stdio(false);
    int n; cin >> n;
    edges.push_back((ed){0,0});
    for(int i=1;i<n;i++){
    int x,y,w;
    cin >> x >> y >> w;
    x++;y++;
    edges.push_back((ed){x,y});
    g[x].push_back((edge){y,w});
    g[y].push_back((edge){x,w});
    }
    dfs1(1,-1,1);
    memset(arr,0,sizeof(arr));
    dfs2(1,1);
    build_tree(1,bh,1);
    int m;cin >> m;
    for(int i=1;i<=m;i++){
    string str; cin >> str;
    if(str[0] == 'C')  A[i].dir = 1;
    if(str[0] == 'N')  A[i].dir = 2;
    if(str[0] == 'S')  A[i].dir = 3;
    if(str[1] == 'A')  A[i].dir = 4;
    if(str[1] == 'I')  A[i].dir = 5;
    int u,v; cin >> u >> v;
    if(A[i].dir!=1)u++,v++;
    A[i].u = u;
    A[i].v = v;
    if(A[i].dir == 1) continue;
    lca[u].push_back((point){v,i});
    lca[v].push_back((point){u,i});
    }
    memset(arr,0,sizeof(arr));
    for(int i=1;i<=n;i++)  pre[i] = i;
    tarjan(1,-1);
    for(int i=1;i<=m;i++){
    if(A[i].dir == 1){
        int u = edges[A[i].u].from;
        int v = edges[A[i].u].to;
        if(fa[v] != u) swap(u,v);
        if(son[u] == v){
        int h = head[v];
        int bg = num[h];
        int ch = dep[u]-dep[h];
        bg = bg + ch;
        change(1,bh,bg,A[i].v,1);
        }else{
        int e = to_fa[v];
        int ne = fto_fa[v];
        g[u][ne].w = A[i].v;
        g[v][e].w = A[i].v;
        }
        continue;
    }
    int lac = get_l[i];
    int s = A[i].u,t = A[i].v;
    if(dep[s]<=dep[t])swap(s,t);
    if(A[i].dir == 2){
        while(s!=lac && dep[s] > dep[lac]){
        int h = head[s];
        if(h == s){
            int e = to_fa[s];
            int ne = fto_fa[s];
            g[fa[s]][ne].w = -g[fa[s]][ne].w;
            g[s][e].w = -g[s][e].w;
            s = fa[s];
            continue;
        }
        int bg = num[h];
        if(dep[h] >= dep[lac]){
            int ch = dep[s]-dep[h]-1;
            int end = bg + ch;
            opp(1,bh,bg,end,1);
            s = h;
        }else{
            bg = num[lac];
            int ch = dep[s]-dep[lac]-1;
            int end = bg + ch;
            opp(1,bh,bg,end,1);
            s = lac;
            break;
        }
        }
        while(t!=lac&&dep[t] > dep[lac]){
        int h = head[t];
        if(h == t){
            int e = to_fa[t];
            int ne = fto_fa[t];
            g[fa[t]][ne].w = -g[fa[t]][ne].w;
            g[t][e].w = -g[t][e].w;
            t = fa[t];
            continue;
        }
        int bg = num[h];
        if(dep[h] > dep[lac]){
            int ch = dep[t]-dep[h]-1;
            int end = bg + ch;
            opp(1,bh,bg,end,1);
            t = h;
        }else{
            bg = num[lac];
            int ch = dep[t]-dep[lac]-1;
            int end = bg+ch;
            opp(1,bh,bg,end,1);
            break;
        }
        }
        continue;
    }
    int &pd = A[i].dir;
    if(pd == 3||pd == 4 ||pd == 5){
        int ans = 0;
        if(pd == 5) ans = INT_MAX;
        if(pd == 4) ans = -INT_MAX;
        while(s!=lac&&dep[s] > dep[lac]){
        int h = head[s];
        if(h == s){
            int e = to_fa[s];
            if(pd == 3) ans += g[s][e].w;
            else if(pd == 4) ans = max(ans,g[s][e].w);
            else ans = min(ans,g[s][e].w);
            s = fa[s];
            continue;
        }
        int bg = num[h];
        if(dep[h] >= dep[lac]){
            int ch = dep[s] - dep[h] - 1;
            int end = bg + ch;
            stru p = get_sum(1,bh,bg,end,1);
            if(pd == 3) ans += p.sum;
            else if(pd == 4) ans = max(ans,p.max);
            else ans = min(ans,p.min);
            s = h;
        }else{
            bg = num[lac];
            int ch = dep[s] - dep[lac] - 1;
            int end = bg + ch;
            stru p = get_sum(1,bh,bg,end,1);
            if(pd == 3) ans += p.sum;
            else if(pd == 4) ans = max(ans,p.max);
            else ans = min(ans,p.min);
            s = lac;
            break;
        }
        }
        while(t!=lac&&dep[t] > dep[lac]){
        int h = head[t];
        if(h == t){
            int e = to_fa[t];
            if(pd == 3) ans += g[t][e].w;
            else if(pd == 4) ans = max(ans,g[t][e].w);
            else ans = min(ans,g[t][e].w);
            t = fa[t];
            continue;
        }
        int bg = num[h];
        if(dep[h] > dep[lac]){
            int ch = dep[t] - dep[h] - 1;
            int end = bg + ch;
            stru p = get_sum(1,bh,bg,end,1);
            if(pd == 3) ans += p.sum;
            else if(pd == 4) ans = max(ans,p.max);
            else ans = min(ans,p.min);
            t = h;
        }else{
            bg = num[lac];
            int ch = dep[t] - dep[lac] - 1;
            int end = bg + ch;
            stru p = get_sum(1,bh,bg,end,1);
            if(pd == 3) ans += p.sum;
            else if(pd == 4) ans = max(ans,p.max);
            else ans = min(ans,p.min);
            break;
        }
        }
        printf("%d
",ans);
    }
    }
    return 0;
}