牛客练习赛16

A.字典序最大的子序列

倒着贪心

#include <bits/stdc++.h>
using namespace std;
char s[111111];
 
int main(){
    string ans = "";
    scanf("%s", s + 1);
    int len = strlen(s + 1);
    ans += s[len];
    for(int i = len - 1; i >= 1; i--){
        if(s[i] >= ans[ans.length()-1]) ans += s[i];
    }
    reverse(ans.begin(), ans.end());
    cout << ans << endl;
    return 0;
}

B.漂亮的树

减个等差

#include <bits/stdc++.h>
using namespace std;
const int maxn = 1e5;
int a[maxn];
map<int, int> cnt;
map<int, int> :: iterator it;
 
int main(){
    int n;
    scanf("%d", &n);
    for(int i = 1; i <= n; ++i) scanf("%d", a + i);
    for(int i = 1; i <= n / 2; ++i){
        a[i] -= i;
        a[n-i+1] -= i;
        cnt[a[i]]++;
        cnt[a[n-i+1]]++;
    }
    if(n % 2) a[n/2+1] -= n/2+1, cnt[a[n/2+1]]++;
    int ans = n;
    for(it = cnt.begin(); it != cnt.end(); it++){
        ans = min(ans, n - (*it).second);
    }
    cout << ans << endl;
    return 0;
}

C.任意点

数连通块

#include <bits/stdc++.h>
using namespace std;
int fa[111];
int Find(int x){
    return fa[x] == x ? x : fa[x] = Find(fa[x]);
}
void Union(int x, int y){
    x = Find(x), y = Find(y);
    fa[x] = y;
}
int xx[111], yy[111];
int main(){
    int n, ans = -1;
    scanf("%d", &n);
    for(int i = 1; i <= n; ++i){
        fa[i] = i;
        scanf("%d %d", xx + i, yy + i);
        for(int j = 1; j < i; ++j)
            if(xx[i] == xx[j] || yy[i] == yy[j]) Union(i, j);
    }
    for(int i = 1; i <= n; ++i){
        if(fa[i] == i) ans++;
    }
    printf("%d
", ans);
    return 0;
}

D.k进制数

模k-1不变

#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
const int maxn = 1e5 + 10;
LL a[maxn], sum[maxn];
map<LL, LL> cnt;
 
int main(){
    LL k, b, n, ans = 0, t = 0, z = 0;
    scanf("%lld %lld %lld", &k, &b, &n);
    for(int i = 1; i <= n; ++i){
        scanf("%lld", a + i);
        sum[i] = (sum[i-1] + a[i]) % (k - 1);
        if(a[i] == 0) t++, z += t;
        else t = 0;
    }
    if(b == 0) ans = z;
    else {
        cnt[0]++;
        for(int i = 1; i <= n; ++i)
            ans += cnt[(sum[i]-b+k-1)%(k-1)], cnt[sum[i]]++;
        if(b == k - 1) ans -= z;
    }
    printf("%lld
", ans);
    return 0;
}

E.求值

找变化点

#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
const int maxn = 1e5 + 10;
LL a[maxn];
set<int> pos, v;
set<int> :: reverse_iterator it;
 
int main(){
    int n;
    scanf("%d", &n);
    for(int i = 1; i <= n; ++i){
        scanf("%d", a + i);
        v.insert(a[i]);
        int tmp = a[i];
        vector<int> cl;
        for(it = pos.rbegin(); it != pos.rend(); it++){
            if((a[*it] | tmp) != tmp) tmp |= a[*it], v.insert(tmp);
            else cl.push_back(*it);
        }
        for(int j = 0; j < cl.size(); j++) pos.erase(cl[j]);
        pos.insert(i);
    }
    printf("%d
", v.size());
    return 0;
}

F.选值

随便加加

#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
const int maxn = 1e5 + 10;
LL a[maxn];
 
int main(){
    int n;
    LL d, ans = 0;
    scanf("%d %lld", &n, &d);
    for(int i = 1; i <= n; ++i){
        scanf("%lld", a + i);
        int j = lower_bound(a + 1, a + 1 + i, a[i] - d) - a;
        ans += (i - j) * (LL)(i - j - 1) / 2;
    }
    cout << ans << endl;
    return 0;
}