快乐树剖
1 #include<cstdio> 2 #include<cstring> 3 #include<algorithm> 4 #define rd read() 5 #define lson nd << 1 6 #define rson nd << 1 | 1 7 using namespace std; 8 9 const int N = 1e4; 10 11 int dep[N], top[N], f[N], son[N], size[N], id[N]; 12 int q, n, head[N], tot, cnt, A[N], a[N]; 13 int sum[N << 2]; 14 15 struct edge { 16 int nxt, to, val; 17 }e[N << 1]; 18 19 int read() { 20 int X = 0, p = 1; char c = getchar(); 21 for(; c > '9' || c < '0'; c = getchar()) if(c == '-') p = -1; 22 for(; c >= '0' && c <= '9'; c = getchar()) X = X * 10 + c - '0'; 23 return X * p; 24 } 25 26 void added(int u, int v, int val) { 27 e[++tot].to = v; 28 e[tot].nxt = head[u]; 29 e[tot].val = val; 30 head[u] = tot; 31 } 32 33 void add(int u, int v, int val) { 34 added(u, v, val); 35 added(v, u, val); 36 } 37 38 void dfs1(int u) { 39 size[u] = 1; 40 for(int i = head[u]; i; i = e[i].nxt) { 41 int nt = e[i].to; 42 if(nt == f[u]) continue; 43 f[nt] = u; dep[nt] = dep[u] + 1; 44 a[nt] = e[i].val; 45 dfs1(nt); 46 size[u] += size[nt]; 47 if(size[nt] > size[son[u]]) son[u] = nt; 48 } 49 } 50 51 void dfs2(int u) { 52 id[u] = ++cnt; 53 A[cnt] = a[u]; 54 if(!son[u]) return; 55 top[son[u]] = top[u]; 56 dfs2(son[u]); 57 for(int i = head[u]; i; i = e[i].nxt) { 58 int nt = e[i].to; 59 if(nt == f[u] || nt == son[u]) continue; 60 top[nt] = nt; 61 dfs2(nt); 62 } 63 } 64 65 void update(int nd) { 66 sum[nd] = sum[lson] + sum[rson]; 67 } 68 69 void build(int l, int r, int nd) { 70 if(l == r) { sum[nd] = A[l]; return;} 71 int mid = (l + r) >> 1; 72 build(l, mid, lson); 73 build(mid + 1, r, rson); 74 update(nd); 75 } 76 77 int trie_sum(int L, int R, int l, int r, int nd) { 78 if(L <= l && r <= R) return sum[nd]; 79 int tmp = 0, mid = (l + r) >> 1; 80 if(L <= mid) tmp += trie_sum(L, R, l, mid, lson); 81 if(mid < R) tmp += trie_sum(L, R, mid + 1, r, rson); 82 return tmp; 83 } 84 85 void sw(int &x, int &y) { 86 x ^= y, y ^= x, x ^= y; 87 } 88 89 int query(int x, int y) { 90 int ans = 0, tmp; 91 for(; top[x] != top[y];) { 92 if(dep[top[x]] < dep[top[y]]) swap(x, y); 93 tmp = trie_sum(id[top[x]], id[x], 1, n, 1); 94 ans += tmp; 95 x = f[top[x]]; 96 } 97 if(dep[x] < dep[y]) swap(x, y); 98 tmp = trie_sum(id[y], id[x], 1, n, 1); 99 ans += tmp - a[y]; 100 return ans; 101 } 102 103 int main() 104 { 105 n = rd; q = rd; 106 for(int i = 1; i < n; ++i) { 107 int x = rd, y = rd, z = rd; 108 add(x, y, z); 109 } 110 dfs1(1); dfs2(1); 111 build(1, n, 1); 112 for(; q; q--) { 113 int x = rd, y = rd; 114 printf("%d ", query(x, y)); 115 } 116 }