D - Island Tour
题目大意
思路解析：
可以发现 1->2->4 整体减1变为5->1->3，
其中2->4的距离等于1->3的距离
其中1->2的距离不等于5->1的距离，则只有当[xj - i] <= 0后的xj - > xj+1 和 xj -> xj-1的距离才会发生改变。所有我们枚举当前需要整体减去i，然后看哪些点会小于等于0，又因为我们可以每次记录上一次i-1的答案，所以我们只需要统计哪些点减i会等于0引起的距离变化。
如果我们通过记录哪些点等于i，可以减少统计答案时，遍历哪些点等于i的过程。
代码实现：
import java.io.*;
import java.math.BigInteger;
import java.util.*;public class Main {public static void main(String[] args) throws IOException {int n = input.nextInt();int m = input.nextInt();Vector<Integer>[] arr = new Vector[200001];for (int i = 0; i < 200001; i++) {arr[i] = new Vector<Integer>();}int[] x = new int[m];long ans = 0;for (int i = 0; i < m; i++) {x[i] = input.nextInt();if (i != 0)ans += Math.abs(x[i] - x[i - 1]);arr[x[i]].add(i);}long res = ans;for (int i = 1; i <= n - 1; i++) {for (int t = 0; t < arr[i].size(); t++) {int j = arr[i].get(t);if (j >= 1){int k = (x[j - 1] - i + n) % n;ans += Math.abs(n - k) - k;}if (j < m - 1){int k = (x[j + 1] - i + n) % n;ans += Math.abs(n - k) - k;}}res = Math.min(ans, res);}out.println(res);out.flush();out.close();br.close();}static PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));static Input input = new Input(System.in);static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));static class Input {public BufferedReader reader;public StringTokenizer tokenizer;public Input(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());}}}
