挑战程序竞赛系列（57）：4.6数列上的分治法

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.StringTokenizer;

public class Main{

    String INPUT = "./data/judge/201709/P1854.txt";

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

    void solve() {
        int T = ni();
        while (T --> 0) {
            String s = ns();
            char[] cs = s.toCharArray();
            int n = cs.length;
            int[] map = new int[32];
            for (int i = 0; i < n; ++i) {
                map[cs[i] - 'a']++;
            }

            int cnt = 0;
            for (int i = 0; i < 32; ++i) {
                if ((map[i] & 1) != 0) {
                    cnt++;
                }
            }

            if (cnt > 1) out.println("Impossible");
            else {
                out.println(divide(cs, 0, n - 1));
            }
        }
    }

    public int divide(char[] cs, int i, int j) {
        if (i >= j) return 0;
        char a = cs[i];
        char b = cs[j];

        if (a == b) {
            return divide(cs, i + 1, j - 1);
        }
        int k = i + 1;
        while (k < j && cs[k] != b) k++;
        int op1 = k - i;

        k = j - 1;
        while (k > i && cs[k] != a) k--;
        int op2 = j - k;

        if (op1 < op2) {
            int tt = op1 + i;
            while (tt != i) {
                swap(cs, tt, tt - 1);
                tt--;
            }
            return op1 + divide(cs, i + 1, j - 1);
        }
        else {
            int tt = j - op2;
            while (tt != j) {
                swap(cs, tt, tt + 1);
                tt++;
            }
            return op2 + divide(cs, i + 1, j - 1);
        }
    }

    public void swap(char[] cs, int i, int j) {
        char tmp = cs[i];
        cs[i] = cs[j];
        cs[j] = tmp;
    }


    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();
        solve();
        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);
        }
    }

    static class ArrayUtils {

        public static void fill(int[][] f, int value) {
            for (int i = 0; i < f.length; ++i) {
                Arrays.fill(f[i], value);
            }
        }

        public static void fill(int[][][] f, int value) {
            for (int i = 0; i < f.length; ++i) {
                fill(f[i], value);
            }
        }

        public static void fill(int[][][][] f, int value) {
            for (int i = 0; i < f.length; ++i) {
                fill(f[i], value);
            }
        }
    }
}