D. Note that the answer exists and unique.
A. Most Unstable Array
找规律发现：
-
\(n = 1\)时为\(0\)；
-
\(n = 2\)时为\(n\)；
-
\(n > 2\)时为\(2n\)；
B. Two Arrays And Swaps
【贪心】依次b数组最大的与a数组最小的交换。
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C. Board Moves
【贪心】【数学】因为\(n\)只能是奇数，所以把集中的点放在正中间即可，然后就是公式推导。
/*
n = 7时的情况：
3333333
3222223
3211123
3210123
3211123
3222223
3333333
*/
D. Note that the answer exists and unique.
【优先队列】【模拟】这题会重载运算符与优先队列的话就只是简单的模拟题：区间大的优先，如果区间大小都一样就按照从左到右的顺序来。
AC代码
A
#include<iostream>
#include<cstdio>
using namespace std;
int T, n, m;
int main()
{
scanf("%d", &T);
while(T--){
scanf("%d %d", &n, &m);
if(n == 1) printf("0\n");
else if(n == 2) printf("%d\n", m);
else printf("%d\n", m * 2);
}
return 0;
}
B
#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;
int T, n, k;
int a[102], b[102];
bool cmp(int a, int b){
return a > b;
}
int main()
{
scanf("%d", &T);
while(T--){
scanf("%d %d", &n, &k);
for(int i = 0; i < n; i++) scanf("%d", &a[i]);
for(int i = 0; i < n; i++) scanf("%d", &b[i]);
sort(a, a + n);
sort(b, b + n, cmp);
int tmp = 0;
for(int i = 0; i < k; i++){
if(a[i] < b[tmp]){
a[i] = b[tmp++];
}
}
int ans = 0;
for(int i = 0; i < n; i++) {
// printf("%d ", a[i]);
ans += a[i];
}
printf("%d\n", ans);
}
return 0;
}
C
#include<iostream>
#include<cstdio>
using namespace std;
typedef long long LL;
LL ans[500005];
void build(){
LL t = 1;
for(LL i = 1; i <= 500000; i += 2){
if(i == 1) ans[i] = 0;
else {
ans[i] += ans[i - 2] + ((i * 4 - 4) * t);
t++;
}
}
}
int main()
{
build();
int T, n;
scanf("%d", &T);
while(T--){
scanf("%d", &n);
printf("%I64d\n", ans[n]);
}
return 0;
}
D
//
#include<iostream>
#include<cstdio>
#include<cstring>
#include<queue>
using namespace std;
int T, n, tmp;
int num[200005];
bool take[200005];
struct node{
int l, r;
};
struct node2{
bool operator() (node a, node b){ // 重载运算符
if(a.r - a.l == b.r - b.l) return a.l > b.l; // 如果区间相等，就先从左边开始
return a.r - a.l < b.r - b.l; // 区间大的优先
}
};
priority_queue<node, vector<node>, node2> q;
void solve(){
while(!q.empty()) q.pop(); // 把上次还没出来的先都出来
q.push({1, n});
while(!q.empty()){
node now = q.top(); q.pop();
if(now.l > now.r) continue ;
if(now.l == now.r){
if(num[now.l] != 0) continue ;
num[now.l] = tmp++;
continue ;
}
if((now.r - now.l + 1) % 2 == 1){
int mid = (now.r + now.l) / 2;
num[mid] = tmp++;
q.push({now.l, mid - 1});
q.push({mid + 1, now.r});
}
else {
int mid = (now.r + now.l - 1) / 2;
num[mid] = tmp++;
q.push({now.l, mid - 1});
q.push({mid + 1, now.r});
}
}
}
int main()
{
scanf("%d", &T);
while(T--){
scanf("%d", &n);
memset(num, 0, sizeof(num));
tmp = 1;
solve();
for(int i = 1; i <= n; i++){
if(i != 1) printf(" ");
printf("%d", num[i]);
}
printf("\n");
}
return 0;
}