Packets

#include <bits/stdc++.h>
using namespace std;
int n, ans;
int main()
{
for (scanf("%d", &n); n; n >>= 1)
++ans;
printf("%d", ans);
}


这个为啥错了

#include <bits/stdc++.h>
using namespace std;
int n;
int main()
{
scanf("%d", &n);
printf("%.0f", floor(log(n) / log(2)) + 1);
}


Reach Median

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const ll N = 2e5 + 7;
ll n, s, m, ans, a[N];
int main()
{
scanf("%lld%lld", &n, &s);
for (ll i = 0; i < n; ++i)
scanf("%lld", &a[i]);
sort(a, a + n);
m = n / 2;
if (a[m] < s)
while (a[m] < s && m < n)
ans += s - a[m++];
else
while (a[m] > s && m >= 0)
ans += a[m--] - s;
printf("%lld", ans);
}


Equalize

l[i]+r[i]之后在所有数里的排名就是原来的排名，回代检验即可。

#include <bits/stdc++.h>
using namespace std;
const int N = 1e6 + 9;
char a[N], b[N];
int n;
int main()
{
scanf("%d%s%s", &n, a, b);
for (int i = n = 0; a[i]; ++i)
if (a[i] != b[i])
{
++n;
if (a[i + 1] != b[i + 1] && a[i] == b[i + 1])
++i;
}
printf("%d", n);
}


Valid BFS?

• BFS 序是关于深度的一个非减序列
• BFS 序是关于父节点深度的一个非减序列

#include <bits/stdc++.h>
using namespace std;
const int N = 1e6 + 9;
unordered_set<int> g[N];
int n, m = 1, a[N];
int main()
{
scanf("%d", &n);
for (int i = 1, x, y; i < n; ++i)
{
scanf("%d%d", &x, &y);
g[x].insert(y);
g[y].insert(x);
}
for (int i = 0; i < n; ++i)
scanf("%d", &a[i]);
for (int i = 0; i < n; ++i)
while (g[a[i]].count(a[m]))
++m;
printf(m == n && a[0] == 1 ? "Yes" : "No");
}


Trips

#include <bits/stdc++.h>
using namespace std;
const int N = 1e6 + 9;
unordered_set<int> se, g[N];
pair<int, int> e[N];
int n, m, k, vis[N], ans[N], cnt[N];
void del(int x)
{
if (g[x].size() < k && se.erase(x))
for (auto y : g[x])
g[y].erase(x), del(y);
}
int main()
{
scanf("%d%d%d", &n, &m, &k);
for (int i = 0; i < m; ++i)
{
int &x = e[i].first, &y = e[i].second;
scanf("%d%d", &x, &y);
g[x].insert(y);
g[y].insert(x);
}
for (int i = 1; i <= n; ++i)
se.insert(i);
for (int i = 1; i <= n; ++i)
del(i);
for (int i = m - 1; ~i; --i)
{
ans[i] = se.size();
if (se.empty())
break;
int &x = e[i].first, &y = e[i].second;
g[x].erase(y);
g[y].erase(x);
del(x);
del(y);
}
for (int i = 0; i < m; ++i)
printf("%d\n", ans[i]);
}