Algorithm exercice, purpose is to print all combinaisons possibles with n numbers (0 < n < 10)
function prototype: void ft_print_combn(int n);
examples: n = 1: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
n = 2: 01, 02, 03, 04, 05, 06, 07, 08, 09, 12, 13, 14, 15, 16, 17, 18, 19, 23, 24, 25, 26, 27, 28, 29, 34, 35, 36, 37, 38, 39, 45, 46, 47, 48, 49, 56, 57, 58, 59, 67, 68, 69, 78, 79, 89
n = 3: 012, 013, 014, 015, 016, 017, 018, 019, 023, 024, 025, 026, 027, 028, 029, 034, 035, 036, 037, 038, 039, 045, 046, 047, 048, 049, 056, 057, 058, 059, 067, 068, 069, 078, 079, 089, 123, 124, 125, 126, 127, 128, 129, 134, 135, 136, 137, 138, 139, 145, 146, 147, 148, 149, 156, 157, 158, 159, 167, 168, 169, 178, 179, 189, 234, 235, 236, 237, 238, 239, 245, 246, 247, 248, 249, 256, 257, 258, 259, 267, 268, 269, 278, 279, 289, 345, 346, 347, 348, 349, 356, 357, 358, 359, 367, 368, 369, 378, 379, 389, 456, 457, 458, 459, 467, 468, 469, 478, 479, 489, 567, 568, 569, 578, 579, 589, 678, 679, 689, 789
n = 4: 0123, 0124, 0125, 0126, 0127, 0128, 0129, 0134, 0135, 0136, 0137, 0138, 0139, 0145, 0146, 0147, 0148, 0149, 0156, 0157, 0158, 0159, 0167, 0168, 0169, 0178, 0179, 0189, 0234, 0235, 0236, 0237, 0238, 0239, 0245, 0246, 0247, 0248, 0249, 0256, 0257, 0258, 0259, 0267, 0268, 0269, 0278, 0279, 0289, 0345, 0346, 0347, 0348, 0349, 0356, 0357, 0358, 0359, 0367, 0368, 0369, 0378, 0379, 0389, 0456, 0457, 0458, 0459, 0467, 0468, 0469, 0478, 0479, 0489, 0567, 0568, 0569, 0578, 0579, 0589, 0678, 0679, 0689, 0789, 1234, 1235, 1236, 1237, 1238, 1239, 1245, 1246, 1247, 1248, 1249, 1256, 1257, 1258, 1259, 1267, 1268, 1269, 1278, 1279, 1289, 1345, 1346, 1347, 1348, 1349, 1356, 1357, 1358, 1359, 1367, 1368, 1369, 1378, 1379, 1389, 1456, 1457, 1458, 1459, 1467, 1468, 1469, 1478, 1479, 1489, 1567, 1568, 1569, 1578, 1579, 1589, 1678, 1679, 1689, 1789, 2345, 2346, 2347, 2348, 2349, 2356, 2357, 2358, 2359, 2367, 2368, 2369, 2378, 2379, 2389, 2456, 2457, 2458, 2459, 2467, 2468, 2469, 2478, 2479, 2489, 2567, 2568, 2569, 2578, 2579, 2589, 2678, 2679, 2689, 2789, 3456, 3457, 3458, 3459, 3467, 3468, 3469, 3478, 3479, 3489, 3567, 3568, 3569, 3578, 3579, 3589, 3678, 3679, 3689, 3789, 4567, 4568, 4569, 4578, 4579, 4589, 4678, 4679, 4689, 4789, 5678, 5679, 5689, 5789, 6789
n = 5: 01234, 01235, 01236, 01237, 01238, 01239, 01245, 01246, 01247, 01248, 01249, 01256, 01257, 01258, 01259, 01267, 01268, 01269, 01278, 01279, 01289, 01345, 01346, 01347, 01348, 01349, 01356, 01357, 01358, 01359, 01367, 01368, 01369, 01378, 01379, 01389, 01456, 01457, 01458, 01459, 01467, 01468, 01469, 01478, 01479, 01489, 01567, 01568, 01569, 01578, 01579, 01589, 01678, 01679, 01689, 01789, 02345, 02346, 02347, 02348, 02349, 02356, 02357, 02358, 02359, 02367, 02368, 02369, 02378, 02379, 02389, 02456, 02457, 02458, 02459, 02467, 02468, 02469, 02478, 02479, 02489, 02567, 02568, 02569, 02578, 02579, 02589, 02678, 02679, 02689, 02789, 03456, 03457, 03458, 03459, 03467, 03468, 03469, 03478, 03479, 03489, 03567, 03568, 03569, 03578, 03579, 03589, 03678, 03679, 03689, 03789, 04567, 04568, 04569, 04578, 04579, 04589, 04678, 04679, 04689, 04789, 05678, 05679, 05689, 05789, 06789, 12345, 12346, 12347, 12348, 12349, 12356, 12357, 12358, 12359, 12367, 12368, 12369, 12378, 12379, 12389, 12456, 12457, 12458, 12459, 12467, 12468, 12469, 12478, 12479, 12489, 12567, 12568, 12569, 12578, 12579, 12589, 12678, 12679, 12689, 12789, 13456, 13457, 13458, 13459, 13467, 13468, 13469, 13478, 13479, 13489, 13567, 13568, 13569, 13578, 13579, 13589, 13678, 13679, 13689, 13789, 14567, 14568, 14569, 14578, 14579, 14589, 14678, 14679, 14689, 14789, 15678, 15679, 15689, 15789, 16789, 23456, 23457, 23458, 23459, 23467, 23468, 23469, 23478, 23479, 23489, 23567, 23568, 23569, 23578, 23579, 23589, 23678, 23679, 23689, 23789, 24567, 24568, 24569, 24578, 24579, 24589, 24678, 24679, 24689, 24789, 25678, 25679, 25689, 25789, 26789, 34567, 34568, 34569, 34578, 34579, 34589, 34678, 34679, 34689, 34789, 35678, 35679, 35689, 35789, 36789, 45678, 45679, 45689, 45789, 46789, 56789
n = 6: 012345, 012346, 012347, 012348, 012349, 012356, 012357, 012358, 012359, 012367, 012368, 012369, 012378, 012379, 012389, 012456, 012457, 012458, 012459, 012467, 012468, 012469, 012478, 012479, 012489, 012567, 012568, 012569, 012578, 012579, 012589, 012678, 012679, 012689, 012789, 013456, 013457, 013458, 013459, 013467, 013468, 013469, 013478, 013479, 013489, 013567, 013568, 013569, 013578, 013579, 013589, 013678, 013679, 013689, 013789, 014567, 014568, 014569, 014578, 014579, 014589, 014678, 014679, 014689, 014789, 015678, 015679, 015689, 015789, 016789, 023456, 023457, 023458, 023459, 023467, 023468, 023469, 023478, 023479, 023489, 023567, 023568, 023569, 023578, 023579, 023589, 023678, 023679, 023689, 023789, 024567, 024568, 024569, 024578, 024579, 024589, 024678, 024679, 024689, 024789, 025678, 025679, 025689, 025789, 026789, 034567, 034568, 034569, 034578, 034579, 034589, 034678, 034679, 034689, 034789, 035678, 035679, 035689, 035789, 036789, 045678, 045679, 045689, 045789, 046789, 056789, 123456, 123457, 123458, 123459, 123467, 123468, 123469, 123478, 123479, 123489, 123567, 123568, 123569, 123578, 123579, 123589, 123678, 123679, 123689, 123789, 124567, 124568, 124569, 124578, 124579, 124589, 124678, 124679, 124689, 124789, 125678, 125679, 125689, 125789, 126789, 134567, 134568, 134569, 134578, 134579, 134589, 134678, 134679, 134689, 134789, 135678, 135679, 135689, 135789, 136789, 145678, 145679, 145689, 145789, 146789, 156789, 234567, 234568, 234569, 234578, 234579, 234589, 234678, 234679, 234689, 234789, 235678, 235679, 235689, 235789, 236789, 245678, 245679, 245689, 245789, 246789, 256789, 345678, 345679, 345689, 345789, 346789, 356789, 456789
n = 7: 0123456, 0123457, 0123458, 0123459, 0123467, 0123468, 0123469, 0123478, 0123479, 0123489, 0123567, 0123568, 0123569, 0123578, 0123579, 0123589, 0123678, 0123679, 0123689, 0123789, 0124567, 0124568, 0124569, 0124578, 0124579, 0124589, 0124678, 0124679, 0124689, 0124789, 0125678, 0125679, 0125689, 0125789, 0126789, 0134567, 0134568, 0134569, 0134578, 0134579, 0134589, 0134678, 0134679, 0134689, 0134789, 0135678, 0135679, 0135689, 0135789, 0136789, 0145678, 0145679, 0145689, 0145789, 0146789, 0156789, 0234567, 0234568, 0234569, 0234578, 0234579, 0234589, 0234678, 0234679, 0234689, 0234789, 0235678, 0235679, 0235689, 0235789, 0236789, 0245678, 0245679, 0245689, 0245789, 0246789, 0256789, 0345678, 0345679, 0345689, 0345789, 0346789, 0356789, 0456789, 1234567, 1234568, 1234569, 1234578, 1234579, 1234589, 1234678, 1234679, 1234689, 1234789, 1235678, 1235679, 1235689, 1235789, 1236789, 1245678, 1245679, 1245689, 1245789, 1246789, 1256789, 1345678, 1345679, 1345689, 1345789, 1346789, 1356789, 1456789, 2345678, 2345679, 2345689, 2345789, 2346789, 2356789, 2456789, 3456789
n = 8: 01234567, 01234568, 01234569, 01234578, 01234579, 01234589, 01234678, 01234679, 01234689, 01234789, 01235678, 01235679, 01235689, 01235789, 01236789, 01245678, 01245679, 01245689, 01245789, 01246789, 01256789, 01345678, 01345679, 01345689, 01345789, 01346789, 01356789, 01456789, 02345678, 02345679, 02345689, 02345789, 02346789, 02356789, 02456789, 03456789, 12345678, 12345679, 12345689, 12345789, 12346789, 12356789, 12456789, 13456789, 23456789
n = 9: 012345678, 012345679, 012345689, 012345789, 012346789, 012356789, 012456789, 013456789, 023456789, 123456789