过了n天补的题解:D

AB就不用说了

C. Obtain The String

思路挺简单的,就是贪心,但是直接贪心的复杂度是O(|s|*|t|),会超时,所以需要用到序列自动机

虽然名字很高端但是就是个数组啦(不过我自己想不到就是了)

next[i][j]表示i之后第一次出现j字符的位置,用这个函数就可以把复杂度降到O(|t|)

#include <cstdio>
#include <cstring>
using namespace std;
const int N = ;
char s[N], t[N];
bool flag[];
int next[N][];
int main() {
int cs;
scanf("%d", &cs);
while (cs--) {
scanf("%s", s);
scanf("%s", t);
int len1 = strlen(t);
int len2 = strlen(s);
int l = , cnt = ;
memset(next, 0xff, sizeof(next));
for (int i = len2 - ; i >= ; i--) {
for (int j = ; j < ; j++)
next[i][j] = next[i + ][j];
next[i][s[i] - 'a'] = i; //递推式很简单
}
int pos = ;
for (int i = ; i < len1; i++) {
pos = next[pos][t[i] - 'a'] + ;
if (pos == ) {
cnt++;
pos = next[][t[i] - 'a'] + ;
if (pos == ) {
cnt = -;
break;
}
}
}
printf("%d\n", cnt);
}
return ;
}

D.Same GCDs

如果知道了gcd(a, b) = gcd(a - b, b) (a > b)就是欧拉函数模板题,可惜不知道

gcd(a, m) = gcd(a + x, m) = k

gcd(a/k, m/k) = gcd(a/k + b, m/k) = 1

刚好就是phi[m/k]的值

#include <cstdio>
using namespace std; long long gcd(long long a, long long b) {
return (a % b == ) ? b : gcd(b, a % b);
} long long GetPhi(long long a) {
long long res = a;
for (long long i = ; i * i <= a; i++) {
if (a % i == ) {
res -= res / i;
while (a % i == )
a = a / i;
}
}
if (a > ) res -= res / a;
return res;
} int main() {
int t;
scanf("%d", &t);
while (t--) {
long long a, m;
scanf("%lld %lld", &a, &m);
long long k = gcd(a, m);
long long ans = GetPhi(m / k);
printf("%lld\n", ans);
}
return ;
}
// gcd(a, m) = gcd(a + x, m) = k
// gcd(a/k, m/k) = gcd(a/k + b, m/k) = 1
// phi[m/k];

E.Permutation Separation

令set1 <= val,set2 =val 为若在pos的位置把序列分成两半,则val:=val + 1的时候[1, pos - 1]加上val对应的cost,[pos, n - 1]就减去这个cost,这个可以用线段树维护

然后有一个坑,把我卡在test 6了很久很久,就是val是从0开始,不是从1开始

#include <cstdio>
#include <algorithm>
using namespace std;
#define g(l, r) (l + r | l != r)
#define o g(l, r)
#define ls g(l, mid)
#define rs g(mid + 1, r)
const int N = * 1e5 + ;
typedef long long ll;
ll pos[N], p, w1, a[N];
ll pre[N], minn[N << ], mark[N << ];
int L, R;
void build(int l, int r) {
if (l == r) {
minn[o] = pre[l];
return ;
}
int mid = l + r >> ;
build(l, mid);
build(mid + , r);
minn[o] = min(minn[ls], minn[rs]);
} inline void PushDown(int l, int r) {
if (mark[o] != ) {
int mid = l + r >> ;
mark[ls] += mark[o];
mark[rs] += mark[o];
minn[ls] = minn[ls] + mark[o];
minn[rs] = minn[rs] + mark[o];
mark[o] = ;
}
} void update(int l, int r, int val) {
if (L > R) return ;
if (L <= l && R >= r) {
minn[o] += val;
mark[o] += val;
return ;
}
PushDown(l, r);
int mid = l + r >> ;
if (L <= mid) update(l, mid, val);
if (R > mid) update(mid + , r, val);
minn[o] = min(minn[ls], minn[rs]);
} int main() {
int n;
scanf("%d", &n);
for (int i = ; i <= n; i++) {
int k;
scanf("%d", &k);
pos[k] = i;
}
for (int i = ; i <= n; i++) {
scanf("%lld", &a[i]);
pre[i] = pre[i - ] + a[i];
}
build(, n - );
ll ans = minn[g(, n - )];
for (int i = ; i <= n; i++) {
L = pos[i], R = n - ;
update(, n - , -a[pos[i]]);
L = , R = pos[i] - ;
update(, n - , a[pos[i]]);
ans = min(ans, minn[g(, n - )]);
}
printf("%lld", ans);
return ;
}

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