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Commit 3216ab1

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2 parents ad29eb4 + 0865b16 commit 3216ab1

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3 files changed

+169
-0
lines changed

3 files changed

+169
-0
lines changed

‎tree/2-fixed-length-paths.cpp‎

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#include <bits/stdc++.h>
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using namespace std;
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using ll = long long;
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const int maxn = 2e5+5;
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bool rem[maxn];
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int n, k1, k2, tmr, sz[maxn], dep[maxn], tin[maxn], tout[maxn], tour[maxn], ft[maxn];
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ll ans;
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vector<int> vs[maxn];
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void upd(int pos, int val) {
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++pos;
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while(pos <= n) ft[pos] += val, pos += pos & (-pos);
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}
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int query(int pos) {
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++pos;
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int ret = 0;
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while (pos > 0) ret += ft[pos], pos &= pos-1;
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return ret;
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}
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void dfs(int v, int p = -1) {
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tour[tin[v] = tmr++] = v;
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sz[v] = 1;
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for(int e: vs[v]) if (e != p && !rem[e]) {
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dep[e] = dep[v] + 1;
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dfs(e, v);
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sz[v] += sz[e];
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}
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tout[v] = tmr;
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}
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int centroid(int v, int p, int tsz) {
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for(int e: vs[v])
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if (e != p && !rem[e] && (sz[e] << 1) > tsz)
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return centroid(e, v, tsz);
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return v;
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}
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void solve(int v) {
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dep[v] = tmr = 0, dfs(v);
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upd(0, 1);
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for(int e: vs[v]) if (!rem[e]) {
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for(int i = tin[e], u; i < tout[e]; i++) {
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u = tour[i];
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ans += query(k2 - dep[u]) - query(k1 - dep[u] - 1);
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}
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for(int i = tin[e]; i < tout[e]; i++) upd(dep[tour[i]], 1);
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}
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for(int e: vs[v]) if (!rem[e]) {
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for(int i = tin[e]; i < tout[e]; i++) upd(dep[tour[i]], -1);
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}
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upd(0, -1);
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}
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void decompose(int v) {
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dep[v] = tmr = 0, dfs(v);
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int c = centroid(v, -1, sz[v]);
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solve(c);
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rem[c] = true;
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for(int e: vs[c]) if (!rem[e]) decompose(e);
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}
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int main(){
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scanf("%d %d %d", &n, &k1, &k2);
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for(int i = 1, x, y; i < n; i++) {
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scanf("%d %d", &x, &y);
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vs[x].emplace_back(y);
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vs[y].emplace_back(x);
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}
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decompose(1);
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printf("%lld\n", ans);
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return 0;
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}
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‎tree/finding-a-centroid.cpp‎

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#include <bits/stdc++.h>
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using namespace std;
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using ll = long long;
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const int maxn = 2e5+5;
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int n, sz[maxn];
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vector<int> vs[maxn];
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void dfs(int v, int p = -1) {
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sz[v] = 1;
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for(int e: vs[v]) if (e != p) dfs(e, v), sz[v] += sz[e];
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}
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int centroid(int v, int p = -1) {
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for(int e: vs[v]) if (e != p && (sz[e] << 1) > n) return centroid(e, v);
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return v;
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}
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int main(){
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scanf("%d", &n);
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for(int i = 1, x, y; i < n; i++) {
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scanf("%d %d", &x, &y);
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vs[x].emplace_back(y);
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vs[y].emplace_back(x);
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}
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dfs(1);
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printf("%d\n", centroid(1));
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return 0;
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}
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‎tree/fixed-length-paths.cpp‎

Lines changed: 63 additions & 0 deletions
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#include <bits/stdc++.h>
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using namespace std;
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using ll = long long;
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const int maxn = 2e5+5;
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bool rem[maxn];
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int n, K, tmr, sz[maxn], tin[maxn], tout[maxn], tour[maxn], dep[maxn], cnt[maxn];
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ll ans = 0;
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vector<int> vs[maxn];
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void dfs(int v, int p = -1) {
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tour[tin[v] = tmr++] = v;
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sz[v] = 1;
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for(int e: vs[v]) if (e != p && !rem[e]) {
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dep[e] = dep[v] + 1;
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dfs(e, v);
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sz[v] += sz[e];
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}
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tout[v] = tmr;
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}
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int centroid(int v, int p, int tsize) {
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for(int e: vs[v])
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if (e != p && !rem[e] && (sz[e] << 1) > tsize)
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return centroid(e, v, tsize);
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return v;
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}
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void solve(int v) {
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dep[v] = tmr = 0, dfs(v);
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cnt[0] = 1;
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for(int e: vs[v]) if (!rem[e]) {
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for(int i = tin[e], u; i < tout[e]; i++) {
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u = tour[i];
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if (dep[u] <= K) ans += cnt[K - dep[u]];
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}
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for(int i = tin[e]; i < tout[e]; i++) ++cnt[dep[tour[i]]];
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}
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for(int e: vs[v]) if (!rem[e]) {
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for(int i = tin[e]; i < tout[e]; i++) cnt[dep[tour[i]]] = 0;
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}
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}
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void decompose(int v) {
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dep[v] = tmr = 0, dfs(v);
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int c = centroid(v, -1, sz[v]);
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solve(c);
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rem[c] = true;
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for(int e: vs[c]) if (!rem[e]) decompose(e);
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}
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int main(){
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scanf("%d %d", &n, &K);
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for(int i = 1, x, y; i<n; i++) {
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scanf("%d %d", &x, &y);
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vs[x].emplace_back(y);
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vs[y].emplace_back(x);
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}
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decompose(1);
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printf("%lld\n", ans);
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return 0;
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}
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