93 lines
2.3 KiB
C++
93 lines
2.3 KiB
C++
#include <bits/stdc++.h>
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using namespace std;
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const int N = 3e5 + 10, M = N << 1;
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int n, k;
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//链式前向星
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int e[M], h[N], idx, w[M], ne[M];
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void add(int a, int b, int c = 0) {
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e[idx] = b, ne[idx] = h[a], w[idx] = c, h[a] = idx++;
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}
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//树上差分模板题【点权】
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int depth[N], f[N][25];
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int dlt[N];
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// 倍增2^k,计算k的办法
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// T = log(n) / log(2) + 1;
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const int T = 22;
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//倍增求 a,b的最近公共祖先
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void bfs(int root) {
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queue<int> q;
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q.push(root);
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depth[root] = 1;
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while (q.size()) {
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int u = q.front();
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q.pop();
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for (int i = h[u]; ~i; i = ne[i]) {
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int j = e[i];
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if (depth[j]) continue;
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depth[j] = depth[u] + 1;
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f[j][0] = u;
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for (int k = 1; k <= T; k++) f[j][k] = f[f[j][k - 1]][k - 1];
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q.push(j);
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}
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}
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}
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int lca(int a, int b) {
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if (depth[a] < depth[b]) swap(a, b);
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for (int k = T; k >= 0; k--)
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if (depth[f[a][k]] >= depth[b])
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a = f[a][k];
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if (a == b) return a;
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for (int k = T; k >= 0; k--)
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if (f[a][k] != f[b][k])
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a = f[a][k], b = f[b][k];
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return f[a][0];
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}
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//前缀和
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void dfs(int u, int fa) {
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for (int i = h[u]; ~i; i = ne[i]) {
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int j = e[i];
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if (j == fa) continue;
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dfs(j, u);
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//遍历完j后，dlt[j]已经被填充好，可以合并计算dlt[u]了
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dlt[u] += dlt[j];
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}
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}
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int main() {
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memset(h, -1, sizeof h);
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scanf("%d %d", &n, &k);
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for (int i = 1; i < n; i++) { // n-1条边
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int a, b;
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scanf("%d %d", &a, &b);
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add(a, b), add(b, a);
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}
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//预处理出lca需要的depth数组+f数组(倍增位置数组)
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bfs(1);
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// k条运输牛奶的路线
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for (int i = 1; i <= k; i++) {
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int a, b;
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scanf("%d %d ", &a, &b);
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int lc = lca(a, b);
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//点差分
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dlt[a]++;
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dlt[b]++;
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//提前就把1减出去了
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dlt[lc]--;
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dlt[f[lc][0]]--;
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}
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//利用前缀和合并差分,此时dlt数组的含义已经不是差分了，而是结果数组了
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dfs(1, 0);
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int res = 0; //找出结果数组中的最大值即是答案
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for (int i = 1; i <= n; i++) res = max(res, dlt[i]);
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printf("%d\n", res);
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return 0;
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} |