A. 整数范围
思路:
签到题。答案: 255 255 255
B. 纯质数
思路:
先用筛法筛出所有的质数,再根据题意判断,模板参考AcWing 数学知识。
代码:
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.StreamTokenizer;public class Main {static final int N = 20211000;static int[] p = new int[N];static boolean[] st = new boolean[N];static int cnt;static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));static PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));static StreamTokenizer in = new StreamTokenizer(br);public static int nextInt() throws IOException {in.nextToken();return (int) in.nval;}public static boolean check(int x) {if (st[x]) return false;while (x != 0) {if (st[x % 10]) return false;x /= 10;}return true;}public static void main(String[] args) {// TODO Auto-generated method stubst[0] = st[1] = true;for (int i = 2; i <= 20210605; i++) {if (!st[i]) p[cnt++] = i;for (int j = 0; p[j] * i <= 20210605; j++) {st[p[j] * i] = true;if (i % p[j] == 0) break;}}int ans = 0;for (int i = 1; i <= 20210605; i++) {if (check(i)) ans++;}out.println(ans);out.flush();}
}
C. 完全日期
思路:
使用Java自带的 LocalDate
类,简化日期计算。
代码:
import java.time.LocalDate;public class Main {static LocalDate start = LocalDate.of(2001, 1, 1);static LocalDate end = LocalDate.of(2021, 12, 31);public static boolean check(LocalDate date) {String dt = date.toString();int res = 0;for (int i = 0; i < dt.length(); i++) {if (Character.isDigit(dt.charAt(i))) {res += dt.charAt(i) - '0';}}int a = (int) Math.sqrt(res);return a * a == res;}public static void main(String[] args) {// TODO Auto-generated method stubint ans = 0;while (start.compareTo(end) <= 0) {if (check(start)) ans++;start = start.plusDays(1);}System.out.println(ans);}}
D. 最小权值
思路:
这个题现在看起来就是一个动态规划的题目,但是当时做的时候没意识到,最后错了。可以用记忆化搜索或者动态规划求。
记忆化搜索:
注意空子树权值为0,所以初始化为0;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.StreamTokenizer;public class Main {static final int N = 2030;static long[] dp = new long[N];static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));static PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));static StreamTokenizer in = new StreamTokenizer(br);public static long dfs(int size) {if (dp[size] != 0 || size == 0) return dp[size];long res = 0x3f3f3f3f3f3f3fl;for (int i = 0; i < size; i++) {int j = size - 1 - i;res = Math.min(res, 1 + 2 * dfs(i) + 3 * dfs(j) + (long)i * i * j);}return dp[size] = res;}public static void main(String[] args) {// TODO Auto-generated method stubSystem.out.println(dfs(2021));}
}
动态规划:
易知状态转移方程为:
d p ( i ) = { 0 i = 0 1 + 2 ∗ d p ( l ) + 3 ∗ d p ( r ) + l ∗ l ∗ r 1 + l + r = i , 0 ≤ l , 0 ≤ r dp(i) = \begin{cases} 0 & i = 0 \\ 1 + 2 * dp(l) + 3 * dp(r) + l * l * r & 1 + l + r = i, 0 \le l, 0 \le r \end{cases} dp(i)={01+2∗dp(l)+3∗dp(r)+l∗l∗ri=01+l+r=i,0≤l,0≤r
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.StreamTokenizer;public class Main {static final int N = 2030;static long[] dp = new long[N];static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));static PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));static StreamTokenizer in = new StreamTokenizer(br);public static void main(String[] args) {// TODO Auto-generated method stubfor (int i = 1; i <= 2021; i++) {dp[i] = 0x3f3f3f3f3f3f3f3fl;for (int j = 0; j < i; j++) {int k = i - 1 - j;dp[i] = Math.min(dp[i], 1 + 2 * dp[j] + 3 * dp[k] + (long) j * j * k);}}System.out.println(dp[2021]);}}
E. 大写
思路:
模拟题,String.toUpperCase()
代码:
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;public class Main {static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));static PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));public static void main(String[] args) throws IOException {// TODO Auto-generated method stubString s = br.readLine();out.println(s.toUpperCase());out.flush();}
}
F. 123
思路:
找规律,我们将数段分割为若干段单调递增的序列,第 i i i 段序列的长度为 i i i,则前 i i i 段序列的总长为 i ∗ ( i + 1 ) / 2 i * (i + 1) / 2 i∗(i+1)/2,先用二分处理出询问的 l l l , r r r 的前面一段序列(也可能就是当前的序列)。
数据范围为 1 0 12 10^{12} 1012,根据前面的分析知二分的区间范围不会超过 2 × 1 0 12 \sqrt{2 ×10^{12}} 2×1012,这里取右边界 r = 1500000 r = 1500000 r=1500000,二分求法如下:
int l = 0, r = 1500000;
while (l < r) {int mid = l + r + 1 >> 1;if ((long)mid * (mid + 1) / 2 <= left) l = mid;else r = mid - 1;
}
由于我们二分的是的 l l l , r r r 的前面一段序列(也可能就是当前的序列),如果 l l l 和 r r r 在二分的序列之后,就要算下在当前序列的和,姑且称作 l l l 和 r r r 的余项和。方法是找到 l l l , r r r 在当前元素的位置:
int lrem = (int) (left - (long)l * (l + 1) / 2);
int rrem = (int) (right - (long)l * (l + 1) / 2);
接着算 l l l 和 r r r 的余项和,
long lsum = (long)lrem * (lrem + 1) / 2;
long rsum = (long)rrem * (rrem + 1) / 2;
因为要求 l l l , r r r 之间一段序列的和, l l l 也包括在其中,所以要算出当前值,如果当前元素在第0号位置,也就相当于他在这一段序列的末尾,值为序列的长度
long lval = lrem == 0 ? l : lrem;
接着我们用二分好的答案算出两端序列之间的和,可以先预处理前缀和:
for (int i = 1; i < N; i++) {sum[i] = (long)i * (i + 1) / 2+ sum[i - 1];
}
两端序列之间的和加上 r r r 的余项和,减去 l l l 的余项和,再减去位置为 l l l 的元素值,即为所求。
res += sum[rr] - sum[ll] - lsum + rsum + lval;
时间复杂度分析,预处理的时间复杂度为 O ( 2 ∗ 1 0 12 ) O(\sqrt{2 * 10^{12}}) O(2∗1012),有 T T T 次询问,每次询问的时间复杂度为 O ( l o g ( 2 ∗ 1 0 12 ) ) O(log(\sqrt{2 * 10^{12}})) O(log(2∗1012)),一个很小的常数,大概 20 20 20 左右,所以总的时间复杂度数量级为 1 0 6 10^6 106,完全够用。
代码:
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.StreamTokenizer;public class Main {static final int N = 1414214;static long[] sum = new long[N];static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));static PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));static StreamTokenizer in = new StreamTokenizer(br);public static int nextInt() throws IOException {in.nextToken();return (int) in.nval;}public static long nextLong() throws IOException {in.nextToken();return (long) in.nval;}public static void main(String[] args) throws IOException {// TODO Auto-generated method stubfor (int i = 1; i < N; i++) {sum[i] = (long)i * (i + 1) / 2 + sum[i - 1];}int t = nextInt();while (t-- != 0) {long l = nextLong();long r = nextLong();out.println(figure(l, r));}out.flush();}public static long figure(long left, long right) {long res = 0;int ll = 0, rr = 0;int l = 0, r = 1500000;while (l < r) {int mid = l + r + 1 >> 1;if ((long)mid * (mid + 1) / 2 <= left) l = mid;else r = mid - 1;}ll = l;int lrem = (int) (left - (long)l * (l + 1) / 2);long lsum = (long)lrem * (lrem + 1) / 2;long lval = lrem == 0 ? l : lrem;l = 0;r = 1500000;while (l < r) {int mid = l + r + 1 >> 1;if ((long)mid * (mid + 1) / 2 <= right) l = mid;else r = mid - 1;}rr = l;int rrem = (int) (right - (long)l * (l + 1) / 2);long rsum = (long)rrem * (rrem + 1) / 2;res += sum[rr] - sum[ll] - lsum + rsum + lval; return res;}}
G. 和与乘积
思路:
要求一段区间和和与乘积相等的话, 1 1 1 在里面 是很重要的,所以我们通过一些列的关于1的处理来解决这个问题。
首先我们只存储非 1 1 1 的数,统计每一个非 1 1 1 的数前连续的1的个数,以及前缀和。
num[i] 表示第i个非1的数
onecnt[i] 第i个非1的数前连续的1的个数
s[i] 包含第i个非1元素的前缀和
进行处理后,上述三个数组的有效长度都是 n − 1 n - 1 n−1,随后求出所有数字的和。然后从第一个非 1 1 1 的数开始枚举,计算当前数字和它后面非 1 1 1 的数的乘积,在计算的过程中,每乘一个数都要判断是否可以构成一组解:
如果说当前的乘积已经大于所有数的和,那一定找不到对应的一组累加和,直接退出即可。
对于乘积小于所有数的和的情况,首先计算出乘积与和的差值 d d d,如果 d = 0 d=0 d=0,则构成一组解,如果说乘积大于差值 ,并且差值小于等于当前区间左右两边相邻的连续的 1 1 1 的和,那此时通过加上左右两边的1也可以构成解。
最后的解就是原序列的长度+符合上述分析的解的个数。
代码:
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.math.BigInteger;
import java.util.StringTokenizer;public class Main {static final int N = 200010;static long[] s = new long[N];static int[] num = new int[N], onecnt = new int[N];static int n = 1, k;static PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));public static void main(String[] args) {// TODO Auto-generated method stubReader reader = new Reader(System.in);k = reader.nextInt();for (int i = 1; i <= k; i++) {int tmp = reader.nextInt();if (tmp == 1) {s[n]++;onecnt[n]++;} else {s[n] += s[n - 1] + tmp;num[n] = tmp;n++;}}// 最后一个非1的数后面可能还有一串1long res = s[n - 1] + onecnt[n];long ans = k;for (int i = 1; i < n; i++) {long p = num[i];for (int j = i + 1; j < n; j++) {p *= num[j];if (p > res) break;/*** s[j]为包含第j个非1元素的前缀和* s[i - 1]为包含第i - 1个非1元素的前缀和* 第i个非1元素前1的个数为onecnt[i]* 则从第i个非1元素和第j个非1元素的和为s[j] - s[i - 1] - onecnt[i]*/long d = p - s[j] + s[i - 1] + onecnt[i];if (d == 0) ans++;else if (onecnt[i] + onecnt[j + 1] >= d && d > 0) {long left = Math.min(d, onecnt[i]);long right = Math.min(d, onecnt[j + 1]);ans += left + right - d + 1;}}}out.println(ans);out.flush();}static class Reader {//自定义快读 Readpublic BufferedReader reader;public StringTokenizer tokenizer;public Reader(InputStream stream) {reader = new BufferedReader(new InputStreamReader(stream), 32768);tokenizer = null;}public String next() {while (tokenizer == null || !tokenizer.hasMoreTokens()) {try {tokenizer = new StringTokenizer(reader.readLine());} catch (IOException e) {throw new RuntimeException(e);}}return tokenizer.nextToken();}public String nextLine() {String str = null;try {str = reader.readLine();} catch (IOException e) {// TODO 自动生成的 catch 块e.printStackTrace();}return str;}public int nextInt() {return Integer.parseInt(next());}public long nextLong() {return Long.parseLong(next());}public Double nextDouble() {return Double.parseDouble(next());}public BigInteger nextBigInteger() {return new BigInteger(next());}}
}
H. 巧克力
思路:
贪心问题的难点就在于如何选择贪心策略,如果按照正常思路,从第一天开始就选择能吃的巧克力,前面几天选择的范围比较大,到了后面几天就相对比较难选了,而且前面的选择会直接影响最后是否会有解以及解的大小,但是前面在选的时候根本无法对其造成的影响进行估计,举个例子:如果从前面开始选,一开始会面临很多种选择,通常会选择最优策略,也就是说保质期能满足当前这一天,并且价格最便宜,但如果存在这样一种巧克力,保质期最长,价格也是最低的,在一开始就把它给用了,到了后面就不能用了,也就是说它原本可以在很多天之后吃就行,现在却在前几天就吃了,吃的时候保质期还有很长的一段事件,到了后面可供选择的巧克力保质期就会越来越短,很可能会出现得不到一个可行方案的情况,对于这种情况,其实把前后选择的巧克力对调一下就能解决,把前面选的保质期长,价格低的巧克力放在后面吃,把后面价格高,保质期短的放在前面吃,通过这样一通分析,我们可以惊奇地发现,正着来不行,我们从后面来貌似就比较合理,这也就引申出了我们的正确的策略:
将所有种类的巧克力按保质期从长到短排序,然后我们从后面几天开始选择吃哪块巧克力,对于第 i i i 天,将所有保质期满足能在第 i i i 天吃的巧克力都找出来,然后对它们按价格从小到大排序,选择价格最低的在第 i i i 天吃,并记录一下这种巧克力已经用掉了几块,如果全部都用掉了,那就不能再用了,这里用到了优先队列来动态维护当天能吃的各种巧克力,当前巧克力吃完就弹出。
代码:
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.StreamTokenizer;
import java.util.Arrays;
import java.util.PriorityQueue;public class Main {static final int N = 100010;static int[] cnt = new int[N];static Node[] chos = new Node[N];static int n, x;static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));static PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));static StreamTokenizer in = new StreamTokenizer(br);static class Node implements Comparable<Node> {int a, b, c;public Node(int a, int b, int c) {this.a = a;this.b = b;this.c = c;}@Overridepublic int compareTo(Node o) {// TODO Auto-generated method stubreturn o.b - this.b;}}public static int nextInt() throws IOException {in.nextToken();return (int) in.nval;}public static void main(String[] args) throws IOException {// TODO Auto-generated method stubx = nextInt();n = nextInt();for (int i = 1; i <= n; i++) {int a = nextInt();int b = nextInt();int c = nextInt();chos[i] = new Node(a, b, c);}Arrays.sort(chos, 1, n + 1);PriorityQueue<Node> heap = new PriorityQueue<Node>((o1, o2) -> {return o1.a - o2.a;});int t = 1;long cost = 0;boolean flag = true;for (int i = x; i >= 1; i--) {while(t <= n && chos[t].b >= i) {heap.add(chos[t]);t++;}if (heap.isEmpty()) {flag = false;break;}Node peek = heap.peek();peek.c--;cost += peek.a;if (peek.c == 0) heap.poll();}if (!flag) cost = -1;out.println(cost);out.flush();}}