4.7后缀数组

10 1 2 2 3 4

拼接： 2 2 3 4 2 2 3 4
反转： 4 3 2 2 4 3 2 2
输出： x o o o x x x x
x表示不可能输出的位置，o表示候选位置，观察发现在候选位置中，最小后缀为2 2 4 3
即为答案。

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.Comparator;
import java.util.StringTokenizer;

public class Main{

    String INPUT = "./data/judge/201709/P3581.txt";

    public static void main(String[] args) throws IOException {
        new Main().run();
    }

    void read() {
        int n = ni();
        int[] a = new int[n];
        for (int i = 0; i < n; ++i) a[i] = ni();
        int[] rev = reverse(a, 0, n - 1);
        SuffixArray sa = new SuffixArray(rev);
        int p1 = 0;
        for (int i = 0; i < n; ++i) {
            p1 = n - sa.sa[i];
            if (p1 >= 1 && n - p1 >= 2) break;
        }

        int m = n - p1;
        rev = reverse(merge(a, p1, n - 1), 0, 2 * m - 1);
        sa = new SuffixArray(rev);
        int p2 = 0;
        for (int i = 0; i <= 2 * m; ++i) {
            p2 = p1 + m - sa.sa[i];
            if (p2 - p1 >= 1 && n - p2 >= 1) break;
        }

        int[] rev1 = reverse(a, 0, p1 - 1);
        int[] rev2 = reverse(a, p1, p2 - 1);
        int[] rev3 = reverse(a, p2, n - 1);
        for (int i = 0; i < n; ++i) {
            if (i >= 0 && i <= p1 - 1) out.println(rev1[i]);
            else if (i >= p1 && i <= p2 - 1) out.println(rev2[i]);
            else out.println(rev3[i]);
        }
    }

    class SuffixArray{
        int k = 1;
        int n;
        Integer[] sa;
        int[] rank, tmp;

        SuffixArray(int[] arra){
            n    = arra.length;
            sa   = new Integer[n + 1];
            rank = new int[n + 1];
            tmp  = new int[n + 1];

            for (int i = 0; i <= n; ++i) {
                sa[i] = i;
                rank[i] = i < n ? arra[i] : -1;
            }

            for (k = 1; k <= n; k *= 2) {
                Arrays.sort(sa, cmp);
                tmp[sa[0]] = 0;
                for (int i = 1; i <= n; ++i) {
                    tmp[sa[i]] = tmp[sa[i - 1]] + (cmp.compare(sa[i - 1], sa[i]) < 0 ? 1 : 0);
                }

                for (int i = 0; i <= n; ++i) {
                    rank[i] = tmp[i];
                }
            }
        }

        private Comparator<Integer> cmp = new Comparator<Integer>() {
            @Override
            public int compare(Integer o1, Integer o2) {
                int i = o1;
                int j = o2;
                if (rank[i] != rank[j]) return rank[i] - rank[j];
                else {
                    int ri = i + k <= n ? rank[i + k] : -1;
                    int rj = j + k <= n ? rank[j + k] : -1;
                    return ri - rj;
                }
            }
        }; 
    }


    void swap(int[] arra, int i, int j) {
        int tmp = arra[i];
        arra[i] = arra[j];
        arra[j] = tmp;
    }

    int[] reverse(int[] a, int i, int j) {
        int n = a.length;
        int[] rev = new int[n];
        for (int k = 0; k < n; ++k) rev[k] = a[k];
        while (i < j) {
            swap(rev, i++, j--);
        }
        return rev;
    }

    int[] merge(int[] a, int i, int j) {
        int n = j - i + 1;
        n += n;
        int[] merge = new int[n];
        for (int k = 0; k < n / 2; ++k) {
            merge[k] = merge[k + n / 2] = a[i + k];
        }
        return merge;
    }


    FastScanner in;
    PrintWriter out;

    void run() throws IOException {
        boolean oj;
        try {
            oj = ! System.getProperty("user.dir").equals("F:\\java_workspace\\leetcode");
        } catch (Exception e) {
            oj = System.getProperty("ONLINE_JUDGE") != null;
        }

        InputStream is = oj ? System.in : new FileInputStream(new File(INPUT));
        in = new FastScanner(is);
        out = new PrintWriter(System.out);
        long s = System.currentTimeMillis();
        read();
        out.flush();
        if (!oj){
            System.out.println("[" + (System.currentTimeMillis() - s) + "ms]");
        }
    }

    public boolean more(){
        return in.hasNext();
    }

    public int ni(){
        return in.nextInt();
    }

    public long nl(){
        return in.nextLong();
    }

    public double nd(){
        return in.nextDouble();
    }

    public String ns(){
        return in.nextString();
    }

    public char nc(){
        return in.nextChar();
    }

    class FastScanner {
        BufferedReader br;
        StringTokenizer st;
        boolean hasNext;

        public FastScanner(InputStream is) throws IOException {
            br = new BufferedReader(new InputStreamReader(is));
            hasNext = true;
        }

        public String nextToken() {
            while (st == null || !st.hasMoreTokens()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (Exception e) {
                    hasNext = false;
                    return "##";
                }
            }
            return st.nextToken();
        }

        String next = null;
        public boolean hasNext(){
            next = nextToken();
            return hasNext;
        }

        public int nextInt() {
            if (next == null){
                hasNext();
            }
            String more = next;
            next = null;
            return Integer.parseInt(more);
        }

        public long nextLong() {
            if (next == null){
                hasNext();
            }
            String more = next;
            next = null;
            return Long.parseLong(more);
        }

        public double nextDouble() {
            if (next == null){
                hasNext();
            }
            String more = next;
            next = null;
            return Double.parseDouble(more);
        }

        public String nextString(){
            if (next == null){
                hasNext();
            }
            String more = next;
            next = null;
            return more;
        }

        public char nextChar(){
            if (next == null){
                hasNext();
            }
            String more = next;
            next = null;
            return more.charAt(0);
        }
    }
}