vector going out of bounds depending on a swap statement

For this piece of code-

vector<int> v{ 417, 929, 845, 462, 675, 175, 73, 867, 14, 201, 777, 407, 80, 882, 785, 563, 209, 261, 776, 362, 730, 74, 649, 465, 353, 801, 503, 154, 998, 286, 520, 692, 68, 805, 835, 210, 819, 341, 564, 215, 984, 643, 381, 793, 726, 213, 866, 706, 97, 538, 308, 797, 883, 59, 328, 743, 694, 607, 729, 821, 32, 672, 130, 13, 76, 724, 384, 444, 884, 192, 917, 75, 551, 96, 418, 840, 235, 433, 290, 954, 549, 950, 21, 711, 781, 132, 296, 44, 439, 164, 401, 505, 923, 136, 317, 548, 787, 224, 23, 185, 6, 350, 822, 457, 489, 133, 31, 830, 386, 671, 999, 255, 222, 944, 952, 637, 523, 494, 916, 95, 734, 908, 90, 541, 470, 941, 876, 264, 880, 761, 535, 738, 128, 772, 39, 553, 656, 603, 868, 292, 117, 966, 259, 619, 836, 818, 493, 592, 380, 500, 599, 839, 268, 67, 591, 126, 773, 635, 800, 842, 536, 668, 896, 260, 664, 506, 280, 435, 618, 398, 533, 647, 373, 713, 745, 478, 129, 844, 640, 886, 972, 62, 636, 79, 600, 263, 52, 719, 665, 376, 351, 623, 276, 66, 316, 813, 663, 831, 160, 237, 567, 928, 543, 508, 638, 487, 234, 997, 307, 480, 620, 890, 216, 147, 271, 989, 872, 994, 488, 291, 331, 8, 769, 481, 924, 166, 89, 824, -4, 590, 416, 17, 814, 728, 18, 673, 662, 410, 727, 667, 631, 660, 625, 683, 33, 436, 930, 91, 141, 948, 138, 113, 253, 56, 432, 744, 302, 211, 262, 968, 945, 396, 240, 594, 684, 958, 343, 879, 155, 395, 288, 550, 482, 557, 826, 598, 795, 914, 892, 690, 964, 981, 150, 179, 515, 205, 265, 823, 799, 190, 236, 24, 498, 229, 420, 753, 936, 191, 366, 935, 434, 311, 920, 167, 817, 220, 219, 741, -2, 674, 330, 909, 162, 443, 412, 974, 294, 864, 971, 760, 225, 681, 689, 608, 931, 427, 687, 466, 894, 303, 390, 242, 339, 252, 20, 218, 499, 232, 184, 490, 4, 957, 597, 477, 354, 677, 691, 25, 580, 897, 542, 186, 359, 346, 409, 655, 979, 853, 411, 344, 358, 559, 765, 383, 484, 181, 82, 514, 582, 593, 77, 228, 921, 348, 453, 274, 449, 106, 657, 783, 782, 811, 333, 305, 784, 581, 746, 858, 249, 479, 652, 270, 429, 614, 903, 102, 378, 575, 119, 196, 12, 990, 356, 277, 169, 70, 518, 282, 676, 137, 622, 616, 357, 913, 161, 3, 589, 327 }; 
int n{v.size()};
for(int i{};i<n;i++){
    if(A.at(i)<=n && A.at(i)>0){
        swap(A.at(A.at(i)-1),A.at(i));
        if(A.at(i)!=A.at(A.at(i)-1)){
            i--;
        }
    }
}

I'm getting a out of bound exception.
terminate called after throwing an instance of 'std::out_of_range'
what(): vector::_M_range_check: __n (which is 588) >= this->size() (which is 418)

I don't see with the included conditions if(A.at(i)<=n && A.at(i)>0), how could I possibly go out of bounds.
Also, if I put the swap statement inside the body of the next if (above i--), I do not get the exception, and the loop runs fine.

Solution

In the first loop iteration:

i is 0
A.at(i) is 417
A.at(A.at(i)-1) is A.at(416) which is 589
Then you swap A.at(0) with A.at(416), so now A.at(0) is 589 and A.at(416) is 417.
Then you execute if(A.at(i)!=A.at(A.at(i)-1)). But since A.at(i)-1 is 588, so this does if(589 != A.at(588)) which accesses out of bounds.

Perhaps you meant to do the if test first, i.e.:

if(A.at(i)<=n && A.at(i)>0){
   if(A.at(i)!=A.at(A.at(i)-1)){
        swap(A.at(A.at(i)-1),A.at(i));
        i--;
    }
}

IMO it would be easier to read to use some aliases, e.g.:

auto& current = A.at(i);

if ( current > 0 && current <= n )
{
    auto& other = A.at(current - 1);
    if ( current != other )
    {
        swap(current, other);
        --i;
    }
}