BZOJ 1602 Usaco2008 Oct 牧场行走 倍增LCA

题目大意

思路

CODE

#define _CRT_SECURE_NO_WARNINGS

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#define MAX 1010
using namespace std;

int head[MAX], total;
int _next[MAX << 1], aim[MAX << 1], length[MAX << 1];

int points, asks;

inline void Add(int x, int y, int len)
{
    _next[++total] = head[x];
    aim[total] = y;
    length[total] = len;
    head[x] = total;
}

int father[MAX][20], len[MAX][20];
int deep[MAX];

void DFS(int x, int last)
{
    deep[x] = deep[last] + 1;
    for(int i = head[x]; i; i = _next[i]) {
        if(aim[i] == last)  continue;
        father[aim[i]][0] = x;
        len[aim[i]][0] = length[i];
        DFS(aim[i], x);
    }
}

void SparseTable()
{
    for(int j = 1; j <= 19; ++j)
        for(int i = 1; i <= points; ++i) {
            father[i][j] = father[father[i][j - 1]][j - 1];
            len[i][j] = len[i][j - 1] + len[father[i][j - 1]][j - 1];
        }
}

inline int GetLCA(int x, int y)
{
    if(deep[x] < deep[y])   swap(x, y);
    int re = 0;
    for(int i = 19; ~i; --i)
        if(deep[father[x][i]] >= deep[y]) {
            re += len[x][i];
            x = father[x][i];
        }
    if(x == y)  return re;
    for(int i = 19; ~i; --i)
        if(father[x][i] != father[y][i]) {
            re += len[x][i] + len[y][i];
            x = father[x][i];
            y = father[y][i];
        }
    re += len[x][0] + len[y][0];
    return re;
}

int main()
{
    cin >> points >> asks;
    for(int x, y, z, i = 1; i < points; ++i) {
        scanf("%d%d%d", &x, &y, &z);
        Add(x, y, z), Add(y, x, z);
    }
    DFS(1, 0);
    SparseTable();
    for(int x, y, i = 1; i <= asks; ++i) {
        scanf("%d%d", &x, &y);
        printf("%d\n", GetLCA(x, y));
    }
    return 0;
}