专栏首页机器学习入门挑战程序竞赛系列(66):4.7字符串匹配(1)

挑战程序竞赛系列(66):4.7字符串匹配(1)

版权声明:本文为博主原创文章,未经博主允许不得转载。 https://blog.csdn.net/u014688145/article/details/77987375

挑战程序竞赛系列(66):4.7字符串匹配(1)

传送门:POJ 3690: Constellations


题意:

给定一个由“*”和“0”组成的,大小为N x M 的匹配对象和T个大小为P x Q的匹配模式。输出在匹配对象中至少出现过一次的匹配模式的个数。

滚动hash算法,又叫做Rabin-karp算法。利用滑动窗口循环计算hash值,复杂度可以控制在O(n)O(n)内。

此题扩展到了二维,先算出每一行对应的窗口大小为Q的hash值,接着在利用每一行已算的hash值,再计算窗口大小为P的hash值。

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.HashMap;
import java.util.Map;
import java.util.StringTokenizer;

public class Main{

    String INPUT = "./data/judge/201709/P3690.txt";

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

    void read() {
        int cnt = 0;
        while (true) {
            int n = ni();
            int m = ni();
            int k = ni();
            int p = ni();
            int q = ni();
            if (n + m + k + p + q == 0) break;
            out.println("Case " + (++cnt) + ": " + solve(n, m, k, p, q));
        }
    }

    int solve(int n, int m, int k, int p, int q) {
        char[][] maps = new char[n][m];
        for (int i = 0; i < n; ++i) {
            maps[i] = ns().toCharArray();
        }

        long L = 1000000007;
        long B = 107;
        long[][] hs = new long[n][m];
        for (int i = 0; i < n; ++i) {
            long pw = 1;
            for (int j = 0; j < q; ++j) {
                hs[i][j] = (j > 0 ? hs[i][j - 1] : 0) * B + maps[i][j];
                pw *= B;
            }

            for (int j = q; j < m; ++j) {
                hs[i][j] = hs[i][j - 1] * B + maps[i][j] - pw * maps[i][j - q]; 
            }
        }

        long[][] hs2 = new long[n][m];
        for (int j = 0; j < m; ++j) {
            long pw = 1;
            for (int i = 0; i < p; ++i) {
                hs2[i][j] = (i > 0 ? hs2[i - 1][j] : 0) * L + hs[i][j];
                pw *= L;
            }

            for (int i = p; i < n; ++i) {
                hs2[i][j] = hs2[i - 1][j] * L + hs[i][j] - pw * hs[i - p][j];
            }
        }

        Map<Long, Integer> mem = new HashMap<Long, Integer>();
        for (int i = 0; i < k; ++i) {
            long num = process(nextCharMap(p, q), p, q, L, B);
            Num.inc(mem, num);
        }

        int cnt = 0;
        for (int i = 0; i < n; ++i) {
            for (int j = 0; j < m; ++j) {
                if (i >= p - 1 && j >= q - 1) {
                    if (mem.containsKey(hs2[i][j])) {
                        cnt += mem.get(hs2[i][j]);
                        mem.remove(hs2[i][j]);
                    }
                }
            }
        }
        return cnt;
    }

    long process(char[][] map, int p, int q, long L, long B) {
        long[][] hs = new long[p][q];
        for (int i = 0; i < p; ++i) {
            for (int j = 0; j < q; ++j) {
                hs[i][j] = (j > 0 ? hs[i][j - 1] : 0) * B + map[i][j];
            }
        }

        for (int j = q - 1; j < q; ++j) {
            for (int i = 0; i < p; ++i) {
                hs[i][j] = (i > 0 ? hs[i - 1][j] : 0) * L + hs[i][j];
            }
        }

        return hs[p - 1][q - 1];
    }

    char[][] nextCharMap(int p, int q){
        char[][] maps = new char[p][q];
        for (int i = 0; i < p; ++i) {
            maps[i] = ns().toCharArray();
        }
        return maps;
    }

    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);
        }
    }

    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);
            }
        }
    }

    static class Num{
        public static <K> void inc(Map<K, Integer> mem, K k){
            if (!mem.containsKey(k)) mem.put(k, 0);
            mem.put(k, mem.get(k) + 1);
        }
    }
}

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