挑战程序竞赛系列（54）：4.4 双端队列（1）

详细代码可以fork下Github上leetcode项目，不定期更新。

练习题如下：

• POJ 2823: Sliding Window

POJ 2823: Sliding Window

好吧，单调队列入门题，关于单调队列可以参考博文：
http://blog.csdn.net/u014688145/article/details/71475303

此处代码参照《挑战》P339，唉，被Java的StringBuilder坑了很久，用数组输出即可，直接StringBuilder会内存溢出。

因为双端队列维护的下标，所以能够很容易的更新队列中的下标，使它始终在滑动窗口所示的范围内。

代码如下：

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/P2823.txt";    public static void main(String[] args) throws IOException {        new Main().run();    }    static final int MAX_N = 1000000 + 16;    int N, K;    int[] nums = new int[MAX_N];    int[] deq  = new int[MAX_N];    void solve() {        N = ni();        K = ni();        for (int i = 0; i < N; ++i) nums[i] = ni();        int[] val = new int[MAX_N];        int s = 0, t = 0;        for (int i = 0; i < N; ++i) {            while ((t - s) > 0 && nums[i] <= nums[deq[t - 1]]) {                t--;            }            deq[t++] = i;            if (i - K + 1 >= 0) {                val[i - K + 1] = nums[deq[s]];                if (deq[s] == i - K + 1) {                    s++;                }            }        }        for (int i = 0; i < N - K + 1; ++i) {            out.print(val[i] + (i + 1 == N - K + 1 ? "\n" : " "));        }        s = 0;        t = 0;        for (int i = 0; i < N; ++i) {            while (t > s && nums[i] >= nums[deq[t - 1]]) {                t--;            }            deq[t++] = i;            if (i - K + 1 >= 0) {                val[i - K + 1] = nums[deq[s]];                if (deq[s] == i - K + 1) {                    s++;                }            }        }        for (int i = 0; i < N - K + 1; ++i) {            out.print(val[i] + (i + 1 == N - K + 1 ? "\n" : " "));        }    }    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);            }        }    }}