HDU-1257
HDU-1257
思路
最少需要的防御系统个数就是最大上升子序列的长度。(Dilworth定理)
这篇blog介绍了Dilworth定理。
Code
\(O(n^2)\)的LIS
#include <bits/stdc++.h>
using namespace std;
#define _u_u_ ios::sync_with_stdio(false), cin.tie(nullptr)
#define cf int _o_o_;cin>>_o_o_;for (int Case = 1; Case <= _o_o_;Case++)
#define SZ(x) (int)(x.size())
inline void _A_A_();
signed main() {_A_A_();return 0;}
using ll = long long;
// #define int long long
const int mod = 1e9 + 7;
const int maxn = 3e4 + 10;
const int N = 210, M = 5010;
const int inf = 0x3f3f3f3f;
int a[maxn], dp[maxn];
inline void _A_A_() {
#ifdef LOCAL
freopen("in.in", "r", stdin);
#endif
_u_u_;
int n;
while (cin >> n) {
for (int i = 1;i <= n;i++) cin >> a[i];
int ans = 1;
for (int i = 1;i <= n;i++) {
dp[i] = 1;
for (int j = 1;j < i;j++) {
if(a[i] > a[j]) dp[i] = max(dp[j] + 1 , dp[i]);
}
ans = max(ans, dp[i]);
}
cout << ans << "\n";
}
}
Code
\(O(nlogn)\)的LIS,非dp,参考
#include <bits/stdc++.h>
using namespace std;
#define _u_u_ ios::sync_with_stdio(false), cin.tie(nullptr)
#define cf int _o_o_;cin>>_o_o_;for (int Case = 1; Case <= _o_o_;Case++)
#define SZ(x) (int)(x.size())
inline void _A_A_();
signed main() {_A_A_();return 0;}
using ll = long long;
// #define int long long
const int mod = 1e9 + 7;
const int maxn = 3e4 + 10;
const int N = 210, M = 5010;
const int inf = 0x3f3f3f3f;
inline void _A_A_() {
#ifdef LOCAL
freopen("in.in", "r", stdin);
#endif
_u_u_;
int n;
while (cin >> n) {
vector<int> res; // 用来存储LIS。
int a;
for (int i = 1;i <= n;i++) {
cin >> a;
int sz = lower_bound(res.begin(),res.end(), a) - res.begin();
if (sz == SZ(res)) {
res.push_back(a);
}
else {
res[sz] = a;
}
}
cout << SZ(res) << "\n";
}
}