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Codeforces Round 889 (Div. 2) (video explanations A - D)
A Dalton the Teacher
#include<bits/stdc++.h>
#define endl '\n'
#define INF 0x3f3f3f3f
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
const int N = 1e5 + 10;
void solve()
{
int n;
cin >> n;
vector<int>a(n + 1);
int ans = 0;
for(int i = 1; i <= n; i ++)
{
cin >> a[i];
if(a[i] == i)
ans ++;
}
cout << (ans + 1) / 2 << endl;
}
signed main()
{
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int t;
cin >> t;
while(t--)
solve();
}
B Longest Divisors Interval
#include<bits/stdc++.h>
#define endl '\n'
#define INF 0x3f3f3f3f
#define int long long
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
const int N = 1e5 + 10;
void solve()
{
int n;
cin >> n;
if(n <= 2)
{
cout << n << endl;
return;
}
for(int i = 1; i <= n; i ++)
{
if((n % i) != 0)
{
cout << i - 1 << endl;
return;
}
}
}
signed main()
{
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int t;
cin >> t;
while(t--)
solve();
}
C2 Dual (hard Version)
#include<bits/stdc++.h>
#define endl '\n'
#define INF 0x3f3f3f3f
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
const int N = 1e5 + 10;
void add_1(vector<int>&a, vector<pii>&ans)
{
for(int i = 0; i < a.size() - 1; i ++)
{
a[i + 1] += a[i];
ans.push_back({
i + 1, i});
}
cout << ans.size() << endl;
for(auto [a, b] : ans)
cout << a + 1 << " " << b + 1 << endl;
return;
}
void add_2(vector<int>&a, vector<pii>&ans)
{
for(int i = a.size() - 1; i >= 1; i --)
{
a[i - 1] += a[i];
ans.push_back({
i - 1, i});
}
cout << ans.size() << endl;
for(auto [a, b]: ans)
cout << a + 1 << " " << b + 1 << endl;
return;
}
void solve()
{
int n;
cin >> n;
vector<int>a(n);
int p_max = 0, p_min = 0;
int cnt_1 = 0, cnt_2 = 0;
vector<pii>ans;
for(int i = 0; i < n; i ++)
{
cin >> a[i];
if(a[p_max] < a[i])
p_max = i;
if(a[p_min] > a[i])
p_min = i;
if(a[i] < 0)
cnt_2 ++;
if(a[i] > 0)
cnt_1 ++;
}
if(a[p_min] >= 0)
{
add_1(a, ans);
return;
}
if(a[p_max] <= 0)
{
add_2(a, ans);
return;
}
if(abs(a[p_max]) >= abs(a[p_min]))
{
if(cnt_2 <= 12)
{
for(int i = 0; i < n; i ++)
{
if(a[i] < 0)
{
a[i] += a[p_max];
ans.push_back({
i, p_max});
}
}
add_1(a, ans);
}
else
{
for(int i = 0; i < 5; i ++)
{
if(abs(a[p_min]) >= abs(a[p_max]))
break;
ans.push_back({
p_min, p_min});
a[p_min] += a[p_min];
}
for(int i = 0; i < n; i ++)
{
if(a[i] > 0)
{
a[i] += a[p_min];
ans.push_back({
i, p_min});
}
}
add_2(a, ans);
}
}
else
{
if(cnt_1 <= 12)
{
for(int i = 0; i < n; i ++)
{
if(a[i] > 0)
{
a[i] += a[p_min];
ans.push_back({
i, p_min});
}
}
add_2(a, ans);
}
else
{
for(int i = 0; i < 5; i ++)
{
if(abs(a[p_max]) >= abs(a[p_min]))
break;
a[p_max] += a[p_max];
ans.push_back({
p_max, p_max});
}
for(int i = 0; i < n; i ++)
{
if(a[i] < 0)
{
a[i] += a[p_max];
ans.push_back({
i, p_max});
}
}
add_1(a, ans);
}
}
}
signed main()
{
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int t;
cin >> t;
while(t--)
solve();
}
D Earn or Unlock
#include<bits/stdc++.h>
#define endl '\n'
#define INF 0x3f3f3f3f
#define int long long
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
const int N = 2e5 + 10;
bitset<N>f;
int n, a[N], sum[N];
void solve()
{
cin >> n;
for(int i = 1; i <= n; i ++)
cin >> a[i];
for(int i = 1; i <= 2 * n; i ++)
sum[i] = sum[i - 1] + a[i];
int ans = 0;
f[1] = 1;
for(int i = 1; i <= 2 * n; i ++)
{
f |= (f << a[i]);
if(f[i])
{
ans = max(sum[i] - i + 1, ans);
f[i] = 0;
}
}
cout << ans << endl;
}
signed main()
{
ios::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
solve();
}