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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);
}
}
}