#include <cstring>
#include <cstdio>
#include <algorithm>int n, m, cnt, q, t, k;
int f[10001], head[100001], p[10001][21], minn[10001][21], deep[10001];
bool vis[10001];
struct node
{int x, y, z;
}tree[100001];
struct Node
{int next, to, val;
}edge[100001];inline void add(int a, int b, int c)
{edge[cnt].val = c;edge[cnt].to = b;edge[cnt].next = head[a];head[a] = cnt++;
}inline int father(int a)
{return a == f[a] ? a : f[a] = father(f[a]);
}inline bool cmp(node a, node b)
{return a.z > b.z;
}void kruskal()
{int i;for(i = 1; i <= m; i++)    scanf("%d %d %d", &tree[i].x, &tree[i].y, &tree[i].z);for(i = 1; i <= n; i++) f[i] = i;std::sort(tree + 1, tree + m + 1, cmp);for(i = 1; i <= m; i++){int fa = father(tree[i].x), fb = father(tree[i].y);if(fa != fb){f[fa] = fb;add(tree[i].x, tree[i].y, tree[i].z);add(tree[i].y, tree[i].x, tree[i].z);}if(k == n - 1) break;}
}void dfs(int i)
{int j;vis[i] = 1;for(j = head[i]; j != -1; j = edge[j].next)if(!vis[edge[j].to]){deep[edge[j].to] = deep[i] + 1;p[edge[j].to][0] = i;minn[edge[j].to][0] = edge[j].val;dfs(edge[j].to);}
}void init()
{int i, j;for(j = 1; (1 << j) <= n; j++)for(i = 1; i <= n; i++){p[i][j] = p[p[i][j - 1]][j - 1];minn[i][j] = std::min(minn[i][j - 1], minn[p[i][j - 1]][j - 1]);}
}int lca(int a, int b)
{int i, j, ret = 707406378;if(deep[a] < deep[b]) std::swap(a, b);for(i = 0; (1 << i) <= deep[a]; i++);i--;for(j = i; j >= 0; j--)if(deep[a] - (1 << j) >= deep[b]){ret = std::min(ret, minn[a][j]);a = p[a][j];}if(a == b) return ret;for(j = i; j >= 0; j--)if(p[a][j] != p[b][j]){ret = std::min(ret, std::min(minn[a][j], minn[b][j]));a = p[a][j];b = p[b][j];}ret = std::min(ret, std::min(minn[a][0], minn[b][0]));return ret;
}int main()
{int i, j, x1, y1;scanf("%d %d", &n, &m);memset(head, -1, sizeof(head));//memset(minn, 127 / 3, sizeof(minn));
    kruskal();for(i = 1; i <= n; i++)if(!vis[i]){deep[i] = 1;dfs(i);}init();scanf("%d", &q);for(i = 1; i <= q; i++){scanf("%d %d", &x1, &y1);if(father(x1) != father(y1)) printf("-1\n");else printf("%d\n", lca(x1, y1));}return 0;}

  1 #include <cstdio>
  2 #include <cstring>
  3 #include <algorithm>
  4
  5 const int MAXN = 10001, MAXM = 50001, INF = 707406378;
  6 int n, m, q, cnt, tot;
  7 int head[MAXM], to[MAXM << 1], next[MAXM << 1], val[MAXM << 1];
  8 int f1[MAXN], f[MAXN][21], min[MAXN][21], deep[MAXN];
  9
 10 struct node
 11 {
 12     int x, y, z;
 13 }p[MAXM];
 14
 15 inline bool cmp(node a, node b)
 16 {
 17     return a.z > b.z;
 18 }
 19
 20 inline void add(int x, int y, int z)
 21 {
 22     to[cnt] = y;
 23     val[cnt] = z;
 24     next[cnt] = head[x];
 25     head[x] = cnt++;
 26 }
 27
 28 inline int find(int x)
 29 {
 30     return x == f1[x] ? x : f1[x] = find(f1[x]);
 31 }
 32
 33 inline int Min(int x, int y)
 34 {
 35     return x < y ? x : y;
 36 }
 37
 38 inline void swap(int &x, int &y)
 39 {
 40     x ^= y ^= x ^= y;
 41 }
 42
 43 inline void dfs(int u)
 44 {
 45     int i, v;
 46     deep[u] = deep[f[u][0]] + 1;
 47     for(i = 0; f[u][i]; i++)
 48         f[u][i + 1] = f[f[u][i]][i],
 49         min[u][i + 1] = Min(min[u][i], min[f[u][i]][i]);
 50     for(i = head[u]; i ^ -1; i = next[i])
 51     {
 52         v = to[i];
 53         if(!deep[v])
 54         {
 55             f[v][0] = u;
 56             min[v][0] = val[i];
 57             dfs(v);
 58         }
 59     }
 60 }
 61
 62 inline int lca(int x, int y)
 63 {
 64     int i, ans = INF;
 65     if(deep[x] < deep[y]) swap(x, y);
 66     for(i = 20; i >= 0; i--)
 67         if(deep[f[x][i]] >= deep[y])
 68             ans = Min(ans, min[x][i]), x = f[x][i];
 69     if(x == y) return ans == INF ? -1 : ans;
 70     for(i = 20; i >= 0; i--)
 71         if(f[x][i] ^ f[y][i])
 72             ans = Min(ans, min[x][i]),
 73             ans = Min(ans, min[y][i]),
 74             x = f[x][i], y = f[y][i];
 75     ans = Min(ans, min[x][0]);
 76     ans = Min(ans, min[y][0]);
 77     return ans == INF ? -1 : ans;
 78 }
 79
 80 int main()
 81 {
 82     //freopen("truck.in", "r", stdin);
 83     //freopen("truck.out", "w", stdout);
 84     int i, x, y, fx, fy;
 85     scanf("%d %d", &n, &m);
 86     memset(head, -1, sizeof(head));
 87     memset(min, 127 / 3, sizeof(min));
 88     for(i = 1; i <= m; i++) scanf("%d %d %d", &p[i].x, &p[i].y, &p[i].z);
 89     std::sort(p + 1, p + m + 1, cmp);
 90     for(i = 1; i <= n; i++) f1[i] = i;
 91     for(i = 1; i <= m; i++)
 92     {
 93         fx = find(p[i].x);
 94         fy = find(p[i].y);
 95         if(fx ^ fy)
 96         {
 97             f1[fx] = fy;
 98             tot++;
 99             add(p[i].x, p[i].y, p[i].z);
100             add(p[i].y, p[i].x, p[i].z);
101         }
102         if(tot == n - 1) break;
103     }
104     for(i = 1; i <= n; i++)
105         if(!deep[i])
106             dfs(i);
107     scanf("%d", &q);
108     for(i = 1; i <= q; i++)
109     {
110         scanf("%d %d", &x, &y);
111         if(find(x) ^ find(y)) puts("-1");
112         else printf("%d\n", lca(x, y));
113     }
114     return 0;
115 }