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Commit 930173a

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another problem
1 parent cc66612 commit 930173a

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2 files changed

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2 files changed

+182
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lines changed

‎tree/2-path-queries-iterative.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, q, tmr, a[maxn], tour[maxn], tin[maxn], dep[maxn], par[maxn], head[maxn], sz[maxn], st[4*maxn];
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vector<int> vs[maxn];
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void dfs(int v) {
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sz[v] = 1;
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for(int i = 0, e; i<int(vs[v].size()); i++) {
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e = vs[v][i];
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if (e == par[v]) {
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swap(vs[v][i--], vs[v].back());
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vs[v].pop_back();
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continue;
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}
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par[e] = v;
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dep[e] = dep[v] + 1;
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dfs(e);
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sz[v] += sz[e];
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if (sz[e] > sz[vs[v][0]]) swap(vs[v][i], vs[v][0]);
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}
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}
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void hld(int v) {
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tour[tmr] = a[v];
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tin[v] = tmr++;
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for(int e : vs[v]) {
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head[e] = e == vs[v][0] ? head[v] : e;
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hld(e);
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}
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}
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//Time limit is very tight for recursive segment tree
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//Passes easily with iterative though.
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void build() {
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for(int i = 0; i<n; i++) st[n + i] = tour[i];
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for(int i = n-1; i>0; i--) st[i] = max(st[i<<1], st[(i<<1)|1]);
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}
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void upd(int i, int v) {
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for(st[i+=n] = v; i > 1; i >>= 1) st[i>>1] = max(st[i], st[i^1]);
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}
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int query(int l, int r) {
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int res = -1;
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for(l += n, r += n+1; l < r; l >>= 1, r >>= 1) {
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if (l&1) res = max(res, st[l++]);
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if (r&1) res = max(res, st[--r]);
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}
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return res;
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}
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int path_query(int u, int v) {
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int res = -1;
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while(head[u] != head[v]) {
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if (dep[head[u]] < dep[head[v]]) swap(u, v);
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res = max(res, query(tin[head[u]], tin[u]));
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u = par[head[u]];
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}
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if (dep[u] < dep[v]) swap(u, v);
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return max(res, query(tin[v], tin[u]));
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}
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int main(){
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scanf("%d %d", &n, &q);
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for(int i = 1; i<=n; i++) scanf("%d", &a[i]);
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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].push_back(y);
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vs[y].push_back(x);
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}
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dfs(1);
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hld(1);
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build();
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for(int i = 0, t, x, y; i<q; i++) {
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scanf("%d %d %d", &t, &x, &y);
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if (t == 1) upd(tin[x], y);
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else printf("%d\n", path_query(x, y));
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}
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return 0;
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}
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‎tree/2-path-queries-recursive.cpp‎

Lines changed: 96 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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int n, q, tmr, a[maxn], tour[maxn], tin[maxn], dep[maxn], par[maxn], head[maxn], sz[maxn], st[4*maxn];
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vector<int> vs[maxn];
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void dfs(int v) {
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sz[v] = 1;
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for(int i = 0, e; i<int(vs[v].size()); i++) {
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e = vs[v][i];
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if (e == par[v]) {
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swap(vs[v][i--], vs[v].back());
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vs[v].pop_back();
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continue;
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}
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par[e] = v;
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dep[e] = dep[v] + 1;
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dfs(e);
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sz[v] += sz[e];
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if (sz[e] > sz[vs[v][0]]) swap(vs[v][i], vs[v][0]);
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}
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}
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void hld(int v) {
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tour[tmr] = a[v];
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tin[v] = tmr++;
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for(int e : vs[v]) {
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head[e] = e == vs[v][0] ? head[v] : e;
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hld(e);
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}
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}
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void build(int pos = 1, int l = 0, int r = n-1) {
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if (l == r) { st[pos] = tour[l]; return; }
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int mid = (l+r) >> 1, child = pos << 1;
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build(child, l, mid);
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build(child|1, mid+1, r);
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st[pos] = max(st[child], st[child|1]);
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}
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//Cheesy query parameters as global variables to squeeze
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//recursive segtree into the time limit. Passes with 0.97s.
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//Just use iterative segment tree instead honestly.
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int qi, ql, qr, qv;
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void upd(int pos = 1, int l = 0, int r = n-1) {
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if (l == r) { st[pos] = qv; return; }
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int mid = (l+r) >> 1, child = pos << 1;
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if (qi <= mid) upd(child, l, mid);
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else upd(child|1, mid+1, r);
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st[pos] = max(st[child], st[child|1]);
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}
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int query(int pos = 1, int l = 0, int r = n-1) {
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if (r < ql or l > qr) return -1;
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if (ql <= l && r <= qr) return st[pos];
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int mid = (l+r) >> 1, child = pos << 1;
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return max(query(child, l, mid), query(child|1, mid+1, r));
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}
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int path_query(int u, int v) {
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int res = -1;
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while(head[u] != head[v]) {
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if (dep[head[u]] < dep[head[v]]) swap(u, v);
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ql = tin[head[u]], qr = tin[u];
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res = max(res, query());
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u = par[head[u]];
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}
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if (dep[u] < dep[v]) swap(u, v);
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ql = tin[v], qr = tin[u];
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return max(res, query());
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}
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int main(){
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scanf("%d %d", &n, &q);
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for(int i = 1; i<=n; i++) scanf("%d", &a[i]);
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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].push_back(y);
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vs[y].push_back(x);
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}
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dfs(1);
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hld(1);
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build();
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for(int i = 0, t, x, y; i<q; i++) {
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scanf("%d %d %d", &t, &x, &y);
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if (t == 1) qi = tin[x], qv = y, upd();
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else printf("%d\n", path_query(x, y));
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}
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return 0;
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}
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