拯救邦德 - 树上递增

Posted 2021-02-09 ak-ls

 

额(⊙o⊙)…，百度翻译是这样的

                     

  

Sample Input

4 5

1 2 10

1 3 20

1 4 100

2 4 30

3 4 10

2

1 4

4 1

 

2 1

1 2 100

1 1 2

Sample Output

20

20

#include <bits/stdc++.h>

using namespace std;

// #define INF 0x3f3f3f3f
#define MAXN 100010
// #define MAXM 5010

inline int read()
{
    int x = 0,ff = 1;char ch = getchar();
    while(!isdigit(ch))
    {
        if(ch == ‘-‘) ff = -1;
        ch = getchar();
    }
    while(isdigit(ch))
    {
        x = (x << 1) + (x << 3) + (ch ^ 48);
        ch = getchar();
    }
    return x * ff;
}

inline void write(int x)
{
    if(x < 0) putchar(‘-‘),x = -x;
    if(x > 9) write(x / 10);
    putchar(x % 10 +‘0‘);
}
 
int a,b,c,cnt = 0,deep[MAXN],fa[MAXN],mxcost[MAXN][50];
int lin[MAXN],tot = 0,p[MAXN][50],cost[MAXN],vis[MAXN];
// queue < int > q;
struct node
{
    int x,y,v;
}m[MAXN];
struct edge
{
    int y,v,next;
}e[MAXN];

inline void add(int xx,int yy,int vv)
{
    e[++tot].y = yy;
    e[tot].v = vv;
    e[tot].next = lin[xx];
    lin[xx] = tot;
}

inline bool cmp(node x,node y)
{
    return x.v < y.v;
}

inline int get(int x)
{
    return fa[x] == x ? x : fa[x] = get(fa[x]);
}

inline void clear()
{
    // queue < int > empty;
    // swap(empty,q);
    tot = 0;
    memset(m,0,sizeof(e));
    memset(lin,0,sizeof(lin));
    memset(e,0,sizeof(e));
    memset(deep,0,sizeof(deep));
    memset(cost,0,sizeof(cost));
    memset(mxcost,0,sizeof(mxcost));
    memset(vis,false,sizeof(vis));
}

void Kruskal()
{
    cnt = 0;
    for(int i = 1;i <= a;++i)
    fa[i] = i;
    sort(m + 1,m + b + 1,cmp);
    for(int i = 1;i <= b && cnt < a - 1;++i)
    {
        int x = get(m[i].x),y = get(m[i].y);
        if(x != y)
        {
            fa[x] = y;
            cnt++;
            add(m[i].x,m[i].y,m[i].v);
            add(m[i].y,m[i].x,m[i].v);
        }
    }
}

void BFS()
{
    queue < int > q;
    memset(fa,0,sizeof(fa));
    deep[1] = 1; q.push(1); fa[1] = -1;
    while(!q.empty())
    {
        int x = q.front(); q.pop();
        for(int i = lin[x],y;i;i = e[i].next)
        {
            if(deep[y = e[i].y]) continue;
            fa[y] = x;
            deep[y] = deep[x] + 1;
            cost[y] = e[i].v;
            q.push(y);
        }
    }
}

void make()
{
    for(int i = 1;i <= a;++i)
    {
        p[i][0] = fa[i]; mxcost[i][0] = cost[i];
        for(int j = 1;(1 << j) <= a;++j)
            p[i][j] = -1;
    }
    for(int i = 1;(1 << i) <= a;++i)
    {
        for(int j = 1;j <= a;++j)
        {
            int y = p[j][i - 1];
            if(y != -1)
            {
                p[j][i] = p[y][i - 1];
                mxcost[j][i] = max(mxcost[j][i - 1],mxcost[y][i - 1]);
            }
        }
    }
}

int lca(int x,int y)
{
    int t = 0,ans = 0;
    if(deep[x] > deep[y]) swap(x , y);
    while((1 << t) <= a) ++t;
    --t;
    for(int i = t;i >= 0;--i)
    if(deep[p[y][i]] >= deep[x]) 
    {
        ans = max(ans,mxcost[y][i]);   
        y = p[y][i];
    }
    if(x == y) return ans;
    for(int i = t;i >= 0;--i)
    {
        if(p[x][i] != p[y][i])
        {
            ans = max(ans,mxcost[x][i]);
            ans = max(ans,mxcost[y][i]);
            x = p[x][i];
            y = p[y][i];
        }
    }
    ans = max(ans,mxcost[x][0]);
    ans = max(ans,mxcost[y][0]);
    return ans;
}

int main()
{
    int T = 0;
    while(scanf("%d%d",&a,&b) == 2)
    {
        clear();
        for(int i = 1;i <= b;++i)
        {   
            m[i].x = read();
            m[i].y = read();
            m[i].v = read();
        }
        Kruskal();
        memset(fa,0,sizeof(fa));
        BFS();
        make();
        c = read();
        if(++T != 1) putchar(‘
‘);
        while(c--)
        {
            int x,y;
            x = read(); y = read();
            write(lca(x,y));putchar(‘
‘);
        }
    }
    return 0;
}

 

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