4 "cell_type": "markdown",
7 "# Subsequence strings\n",
9 "Given two strings `a` and `b`, is `a` a subsequence of `b`?\n",
14 "b = \"dabaabcacb\",\n",
16 "return True : dAbAaBCaCb\n",
29 "s2t = \"dabaabcacb\"\n",
36 "cell_type": "markdown",
39 "`dp_table[i, j]` is True if first `i` characters of `s1` can be found in first `j` characters of `s2`."
106 " (4, 10): False,\n",
120 "execution_count": 2,
122 "output_type": "execute_result"
126 "dp_table = {(i, j): False\n",
127 " for i in range(len(s1)+1)\n",
128 " for j in range(len(s2)+1)}\n",
134 "execution_count": 3,
140 "def show_table(table):\n",
141 " return '\\n'.join(\n",
142 " ' '.join(str(table[i, j])[0] for j in sorted(set([k[1] for k in table])))\n",
143 " for i in sorted(set([k[0] for k in table]))) "
148 "execution_count": 4,
153 "output_type": "stream",
155 "F F F F F F F F F F F\n",
156 "F F F F F F F F F F F\n",
157 "F F F F F F F F F F F\n",
158 "F F F F F F F F F F F\n",
159 "F F F F F F F F F F F\n",
160 "F F F F F F F F F F F\n"
165 "print(show_table(dp_table))"
170 "execution_count": 5,
175 "output_type": "stream",
210 "xx 4 4 a b False\n",
224 "{(1, 1): (0, 0, 'a', 's1'),\n",
225 " (1, 2): (0, 1, 'a', 's1'),\n",
226 " (1, 3): (0, 2, 'a', 's1'),\n",
227 " (1, 4): (1, 3, 'b', 's2'),\n",
228 " (1, 5): (0, 4, 'a', 's1'),\n",
229 " (1, 6): (1, 5, 'b', 's2'),\n",
230 " (1, 7): (1, 6, 'b', 's2'),\n",
231 " (2, 2): (1, 1, 'a', 's1'),\n",
232 " (2, 3): (1, 2, 'a', 's1'),\n",
233 " (2, 4): (2, 3, 'b', 's2'),\n",
234 " (2, 5): (1, 4, 'a', 's1'),\n",
235 " (2, 6): (2, 5, 'b', 's2'),\n",
236 " (2, 7): (2, 6, 'b', 's2'),\n",
237 " (3, 3): (2, 2, 'a', 's1'),\n",
238 " (3, 4): (3, 3, 'b', 's2'),\n",
239 " (3, 5): (2, 4, 'a', 's1'),\n",
240 " (3, 6): (3, 5, 'b', 's2'),\n",
241 " (3, 7): (3, 6, 'b', 's2'),\n",
242 " (4, 5): (3, 4, 'a', 's1'),\n",
243 " (4, 6): (4, 5, 'b', 's2'),\n",
244 " (4, 7): (4, 6, 'b', 's2')}"
247 "execution_count": 5,
249 "output_type": "execute_result"
260 "dp_table = {(i, j): False\n",
261 " for i in range(len(s1)+1)\n",
262 " for j in range(len(s2)+1)}\n",
264 "backpointers = {}\n",
266 "for i in range(len(s1)+1):\n",
267 " for j in range(i, len(s2)+1):\n",
268 " if i == 0 or j == 0:\n",
269 " dp_table[i, j] = True\n",
270 " print('aa', i, j, '!', '!', dp_table[i, j])\n",
272 " # extend by character from s2\n",
273 " if dp_table[i, j-1]:\n",
274 " dp_table[i, j] = True\n",
275 " backpointers[i, j] = (i, j-1, s2[j-1], 's2')\n",
276 " print('s2', i, j, s1[i-1], s2[j-1], dp_table[i, j]) \n",
277 " # extend by character from s1\n",
278 " if dp_table[i-1, j-1] and s1[i-1] == s2[j-1]:\n",
279 " dp_table[i, j] = True\n",
280 " backpointers[i, j] = (i-1, j-1, s1[i-1], 's1') \n",
281 " print('s1', i, j, s1[i-1], s2[j-1], dp_table[i, j])\n",
282 " if not dp_table[i, j]:\n",
283 " print('xx', i, j, s1[i-1], s2[j-1], dp_table[i, j])\n",
285 "print(show_table(dp_table))\n",
291 "execution_count": 13,
297 "def show_backtrace(bps):\n",
298 " i = max([0] + [k[0] for k in bps])\n",
299 " j = max([0] + [k[1] for k in bps])\n",
301 " if (i, j) in bps:\n",
302 " while i != 0 and j != 0:\n",
303 " if bps[i, j][3] == 's1':\n",
304 " chars += bps[i, j][2].upper()\n",
306 " chars += bps[i, j][2]\n",
307 " i, j = bps[i, j][0], bps[i, j][1] \n",
308 " return ''.join(list(reversed(chars)))\n",
315 "execution_count": 7,
324 "execution_count": 7,
326 "output_type": "execute_result"
330 "show_backtrace(backpointers)"
335 "execution_count": 28,
340 "output_type": "stream",
352 "aa 0 10 ! ! True\n",
353 "xx 1 1 a d False\n",
365 "s2 1 10 a b True\n",
366 "xx 2 2 a a False\n",
367 "xx 2 3 a b False\n",
376 "s2 2 10 a b True\n",
377 "xx 3 3 a b False\n",
378 "xx 3 4 a a False\n",
385 "s2 3 10 a b True\n",
386 "xx 4 4 a a False\n",
387 "xx 4 5 a a False\n",
388 "xx 4 6 a b False\n",
389 "xx 4 7 a c False\n",
401 "execution_count": 28,
403 "output_type": "execute_result"
407 "is_subseq(s1, s2t, debug=True)"
412 "execution_count": 27,
418 "def is_subseq(seq1, seq2, return_backpointers=False, return_table=False, debug=False):\n",
419 " \"\"\"Return true if seq1 is a subsequence of seq2.\n",
420 " If return_backpointers, also return the set of backpointers to\n",
421 " reconstruct the subsequence\"\"\"\n",
423 " # dp_table[i, j] is True if first i characters of seq1 can\n",
424 " # be found in the first j characters of seq2\n",
426 " dp_table = {(i, j): False\n",
427 " for i in range(len(seq1)+1)\n",
428 " for j in range(len(seq2)+1)}\n",
430 " backpointers = {}\n",
432 " for i in range(len(seq1)+1):\n",
433 " for j in range(i, len(seq2)+1):\n",
434 " if i == 0 or j == 0:\n",
435 " dp_table[i, j] = True\n",
436 " if debug: print('aa', i, j, '!', '!', dp_table[i, j])\n",
438 " # extend by character from s2\n",
439 " if dp_table[i, j-1]:\n",
440 " dp_table[i, j] = True\n",
441 " backpointers[i, j] = (i, j-1, seq2[j-1], 's2')\n",
442 " if debug: print('s2', i, j, seq1[i-1], seq2[j-1], dp_table[i, j]) \n",
443 " # extend by character from s1\n",
444 " if dp_table[i-1, j-1] and seq1[i-1] == seq2[j-1]:\n",
445 " dp_table[i, j] = True\n",
446 " backpointers[i, j] = (i-1, j-1, seq1[i-1], 's1') \n",
447 " if debug: print('s1', i, j, seq1[i-1], seq2[j-1], dp_table[i, j])\n",
448 " if not dp_table[i, j]:\n",
449 " if debug: print('xx', i, j, seq1[i-1], seq2[j-1], dp_table[i, j]) \n",
451 "# if return_backpointers:\n",
452 "# return dp_table[len(seq1), len(seq2)], backpointers\n",
454 "# return dp_table[len(seq1), len(seq2)]\n",
456 " if return_backpointers or return_table:\n",
457 " retval = [dp_table[len(seq1), len(seq2)]]\n",
458 " if return_backpointers:\n",
459 " retval += [backpointers]\n",
460 " if return_table:\n",
461 " retval += [dp_table]\n",
462 " return tuple(retval)\n",
464 " return dp_table[len(seq1), len(seq2)]"
469 "execution_count": 37,
475 "def show_annotated_table(table, bps):\n",
476 " return '\\n'.join(' '.join('.' if (i, j) not in bps else bps[i, j][2] if table[i, j] else '.' for j in sorted(set([k[1] for k in table])))\n",
477 " for i in sorted(set([k[0] for k in table])))"
482 "execution_count": 29,
491 "execution_count": 29,
493 "output_type": "execute_result"
497 "tf, bps, tb = is_subseq(s1, s2t, return_backpointers=True, return_table=True)\n",
503 "execution_count": 20,
512 "execution_count": 20,
514 "output_type": "execute_result"
518 "show_backtrace(bps)"
523 "execution_count": 32,
528 "output_type": "stream",
530 "T T T T T T T T T T T\n",
531 "F F T T T T T T T T T\n",
532 "F F F F T T T T T T T\n",
533 "F F F F F T T T T T T\n",
534 "F F F F F F F F T T T\n"
539 "print(show_table(tb))"
544 "execution_count": 38,
549 "output_type": "stream",
551 ". . . . . . . . . . .\n",
552 ". . a b a a b c a c b\n",
553 ". . . . a a b c a c b\n",
554 ". . . . . a b c a c b\n",
555 ". . . . . . . . a c b\n"
560 "print(show_annotated_table(tb, bps))"
565 "execution_count": 21,
574 "execution_count": 21,
576 "output_type": "execute_result"
580 "len(show_backtrace(bps)) == len(s2t)"
585 "execution_count": 24,
591 "('aaaa', 'dabaabcacb')"
594 "execution_count": 24,
596 "output_type": "execute_result"
605 "execution_count": 23,
611 "{(1, 2): (0, 1, 'a', 's1'),\n",
612 " (1, 3): (1, 2, 'b', 's2'),\n",
613 " (1, 4): (0, 3, 'a', 's1'),\n",
614 " (1, 5): (0, 4, 'a', 's1'),\n",
615 " (1, 6): (1, 5, 'b', 's2'),\n",
616 " (1, 7): (1, 6, 'c', 's2'),\n",
617 " (1, 8): (0, 7, 'a', 's1'),\n",
618 " (1, 9): (1, 8, 'c', 's2'),\n",
619 " (1, 10): (1, 9, 'b', 's2'),\n",
620 " (2, 4): (1, 3, 'a', 's1'),\n",
621 " (2, 5): (1, 4, 'a', 's1'),\n",
622 " (2, 6): (2, 5, 'b', 's2'),\n",
623 " (2, 7): (2, 6, 'c', 's2'),\n",
624 " (2, 8): (1, 7, 'a', 's1'),\n",
625 " (2, 9): (2, 8, 'c', 's2'),\n",
626 " (2, 10): (2, 9, 'b', 's2'),\n",
627 " (3, 5): (2, 4, 'a', 's1'),\n",
628 " (3, 6): (3, 5, 'b', 's2'),\n",
629 " (3, 7): (3, 6, 'c', 's2'),\n",
630 " (3, 8): (2, 7, 'a', 's1'),\n",
631 " (3, 9): (3, 8, 'c', 's2'),\n",
632 " (3, 10): (3, 9, 'b', 's2'),\n",
633 " (4, 8): (3, 7, 'a', 's1'),\n",
634 " (4, 9): (4, 8, 'c', 's2'),\n",
635 " (4, 10): (4, 9, 'b', 's2')}"
638 "execution_count": 23,
640 "output_type": "execute_result"
649 "execution_count": null,
658 "execution_count": null,
662 "is_subseq('aaaa', 'aaababb', return_backpointers=True, debug=True)"
667 "execution_count": null,
677 "display_name": "Python 3",
678 "language": "python",
686 "file_extension": ".py",
687 "mimetype": "text/x-python",
689 "nbconvert_exporter": "python",
690 "pygments_lexer": "ipython3",