一种寻找所有解决方案的分代算法
思想
在每个字符串中,最后一个字符只能对有限数量的连续组成部分产生贡献。
末尾的0只能增加一行:
10 + 0 => 100
自从在
00 + 0 => 000
这只是一个重复。如果它增加了那个最小的运行,下一个可能增加的最小运行是
110010 + 0 => 1100100
再次注意
010010 + 0 => 0100100
不是额外的运行,而是重复。下一个可能的添加是
111001001100100
1111001001100100111001001100100
...
数字可能会有所不同,但最小长度为
3, 7, 15, 31
which is
4^1 - 1, 4^2 - 1, ..., 4^n - 1
在字符串开头,不需要使用不同的字符,因此:
maxaddlast = 4^n - 2
通过添加最后一个字符,获得可以添加的最大运行次数。
算法
- 在查找长度为 n 的过程中,所有变量都记录了在 [maxNumberOfRuns - maxaddlast(n+1), maxNumberOfRuns] 范围内的运行计数。
- 要找到 n+1 的最大运行次数解决方案,只需将所有记录的变量扩展为 0 和 1 并进行检查即可。
种子
剩余的问题是调整堆栈大小以收集所有未来种子所需的变量。
由于没有足够的数据来猜测一个有效的公式,选择自适应算法:
- n 的初始堆栈大小从 n - 1 中猜测。
- 对于每个解决方案,检查使用的堆栈大小,确保堆栈始终有一个空间。
- 如果某些 n 中的堆栈已完全使用,则增加堆栈大小并重新开始计算 n。
结果
length 104 with 91 runs
如果默认设置下在600秒内无法达到目标,则会用完内存。请使用-Xmx16G或更多。对于更大的数字,代码必须进行修改以将种子保留在磁盘而非内存中。
它比蛮力法要快得多。
** 代码 **
这是我在Java中的示例代码:
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileWriter;
import java.util.ArrayList;
import de.bb.util.Pair;
public class MaxNumberOfRunsAdaptive {
private static long start;
private ArrayList<Pair<byte[], ArrayList<Integer>>> seed = new ArrayList<>();
private int max;
private ArrayList<ArrayList<Pair<byte[], ArrayList<Integer>>>> nextSeedStack;
private ArrayList<Integer> maxs = new ArrayList<>();
private ArrayList<Integer> diffs = new ArrayList<>();
private ArrayList<Integer> totals = new ArrayList<>();
private int total;
private byte[] buffer;
public static void main(String[] args) {
int limit = 9999;
if (args.length == 1) {
try {
limit = Integer.parseInt(args[0]);
} catch (Exception e) {
}
}
start = System.currentTimeMillis();
new MaxNumberOfRunsAdaptive().run(limit);
long took = (System.currentTimeMillis() - start) / 100;
System.out.println("took " + (took / 10.) + "s");
}
private void run(int limit) {
maxs.add(0);
maxs.add(0);
diffs.add(0);
diffs.add(1);
totals.add(0);
totals.add(0);
ArrayList<Integer> n0 = new ArrayList<Integer>();
n0.add(0);
seed.add(Pair.makePair(new byte[] { '0' }, n0));
saveSeed(2);
for (int i = 2; i <= limit;) {
int restart = compose(i);
if (restart < i) {
System.out.println("*** restarting at: " + restart + " ***");
i = restart;
loadSeed(i);
total = totals.get(i - 1);
} else {
saveSeed(i + 1);
++i;
}
}
}
private void loadSeed(int length) {
try {
seed.clear();
final FileReader fr = new FileReader("seed-" + length + ".txt");
final BufferedReader br = new BufferedReader(fr);
for (String line = br.readLine(); line != null; line = br.readLine()) {
final int space = line.indexOf(' ');
final byte[] b = line.substring(0, space).getBytes();
final String sends = line.substring(space + 2, line.length() - 1);
final ArrayList<Integer> ends = new ArrayList<>();
for (final String s : sends.split(",")) {
ends.add(Integer.parseInt(s.trim()));
}
seed.add(Pair.makePair(b, ends));
}
fr.close();
} catch (Exception e) {
throw new RuntimeException(e);
}
}
private void saveSeed(int length) {
try {
final FileWriter fos = new FileWriter("seed-" + length + ".txt");
for (final Pair<byte[], ArrayList<Integer>> p : seed) {
fos.write(new String(p.getFirst()) + " " + p.getSecond().toString() + "\n");
}
fos.close();
} catch (Exception e) {
throw new RuntimeException(e);
}
}
private int compose(int length) {
max = 0;
int nextStackSize;
if (diffs.size() > length)
nextStackSize = diffs.get(length) + 1;
else
nextStackSize = diffs.get(length - 1) - 1;
if (nextStackSize < 2)
nextStackSize = 2;
nextSeedStack = new ArrayList<>();
for (int i = 0; i < nextStackSize; ++i) {
nextSeedStack.add(new ArrayList<Pair<byte[], ArrayList<Integer>>>());
}
buffer = new byte[length];
for (Pair<byte[], ArrayList<Integer>> e : seed) {
final byte[] s = e.getFirst();
System.arraycopy(s, 0, buffer, 0, length - 1);
if (s.length < 3 || s[s.length - 1] == '1' || s[s.length - 2] == '1' || s[s.length - 3] == '1') {
buffer[length - 1] = '0';
test(length, e.getSecond());
}
if (s.length < 3 || s[s.length - 1] == '0' || s[s.length - 2] == '0' || s[s.length - 3] == '0') {
buffer[length - 1] = '1';
test(length, e.getSecond());
}
}
long took = (System.currentTimeMillis() - start) / 100;
final ArrayList<String> solutions = new ArrayList<String>();
for (Pair<byte[], ArrayList<Integer>> p : nextSeedStack.get(nextSeedStack.size() - 1)) {
solutions.add(new String(p.getFirst()));
}
total += solutions.size();
if (totals.size() <= length)
totals.add(0);
totals.set(length, total);
if (maxs.size() <= length) {
maxs.add(0);
}
maxs.set(length, max);
System.out.println(length + " " + max + " " + (took / 10.) + " " + total + " " + solutions);
seed.clear();
for (ArrayList<Pair<byte[], ArrayList<Integer>>> t : nextSeedStack) {
seed.addAll(t);
}
if (diffs.size() <= length) {
diffs.add(1);
}
int restart = length;
for (final String b : solutions) {
for (int i = 2; i < b.length(); ++i) {
int diff = maxs.get(i) - countRuns(b.substring(0, i));
if (diff >= diffs.get(i)) {
if (i < restart)
restart = i;
diffs.set(i, diff + 1);
}
}
}
System.out.println(diffs);
return restart;
}
void test(final int l, final ArrayList<Integer> endRuns) {
final ArrayList<Integer> r = incrementalCountRuns(l, endRuns);
final int n = r.get(r.size() - 1);
while (max < n) {
nextSeedStack.remove(0);
nextSeedStack.add(new ArrayList<Pair<byte[], ArrayList<Integer>>>());
++max;
}
final int index = nextSeedStack.size() - 1 - max + n;
if (index >= 0)
nextSeedStack.get(index).add(Pair.makePair(buffer.clone(), r));
}
private ArrayList<Integer> incrementalCountRuns(final int l, final ArrayList<Integer> endRuns) {
final ArrayList<Integer> res = new ArrayList<Integer>();
int sz = endRuns.size();
int n = endRuns.get(--sz);
int pos = 0;
for (int i = l - 2; i >= 0; i -= 2) {
int p = (l - i) / 2;
if (equals(buffer, i, buffer, i + p, p)) {
while (i > 0 && buffer[i - 1] == buffer[i - 1 + p]) {
--i;
}
int lasti = -1;
while (pos < sz) {
lasti = endRuns.get(pos);
if (lasti <= i)
break;
lasti = -1;
++pos;
}
if (lasti != i)
++n;
res.add(i);
}
}
res.add(n);
return res;
}
public final static boolean equals(byte a[], int aOff, byte b[], int bOff, int len) {
if (a == null || b == null)
return a == b;
while (len-- > 0)
if (a[aOff + len] != b[bOff + len])
return false;
return true;
}
static int countRuns(String s) {
int n = 0;
int l = s.length();
for (int i = 0; i < l - 1; ++i) {
for (int k = i + 1; k < l; ++k) {
int p = 0;
while (i + p < k && k + p < l) {
if (s.charAt(i + p) != s.charAt(k + p))
break;
++p;
}
if (i + p == k) {
int jj = k + p - 1;
if (i > 0 && s.charAt(i - 1) == s.charAt(i - 1 + p)) {
continue;
}
while (jj + 1 < l && s.charAt(jj + 1) == s.charAt(jj + 1 - p)) {
++jj;
++k;
}
++n;
}
}
}
return n;
}
}