Discussion on: Solution: Remove All Adjacent Duplicates in String II

// Example: S = "aabbbcdddcc", K = 3


         i,j                             // i, j start at 1
S  = [ a, A, b, b, b, c, d, d, d, c, c ] // S[j] overwrites S[i]
st = [ 0 ]                               // S[i] == S[i-1], no change


          ->i,j                          // i, j move up 1
S  = [ a, a, B, b, b, c, d, d, d, c, c ] // S[j] overwrites S[i]
st = [ 0, 2 ]                            // S[i] != S[i-1], st.push(i)


             ->i,j                       // i, j move up 1
S  = [ a, a, b, B, b, c, d, d, d, c, c ] // S[j] overwrites S[i]
st = [ 0, 2 ]                            // S[i] == S[i-1], no change


                ->i,j                    // i, j move up 1
S  = [ a, a, b, b, B, c, d, d, d, c, c ] // S[j] overwrites S[i]
st = [ 0, 2 ]                            // S[i] == S[i-1], no change
          i<-------j                     // i moves back because...
S  = [ a, a, B--B--B, c, d, d, d, c, c ] // ...3 b's found, so...
st = [ 0 ]                               // ...i = st.pop() - 1


           ->i      ->j                  // i, j move up 1
S  = [ a, a, C<-------C, d, d, d, c, c ] // S[j] overwrites S[i]
st = [ 0, 2 ]                            // new letter, st.push(i)


              ->i      ->j               // i, j move up 1
S  = [ a, a, c, D<-------D, d, d, c, c ] // S[j] overwrites S[i]
st = [ 0, 2, 3 ]                         // new letter, st.push(i)


                 ->i      ->j            // i, j move up 1
S  = [ a, a, c, d, D<-------D, d, c, c ] // S[j] overwrites S[i]
st = [ 0, 2, 3 ]                         // S[i] == S[i-1], no change


                    ->i      ->j         // i, j move up 1
S  = [ a, a, c, d, d, D<-------D, c, c ] // S[j] overwrites S[i]
st = [ 0, 2, 3 ]                         // S[i] == S[i-1], no change
             i<--------        j         // i moves back because...
S  = [ a, a, c, D--D--D,  ,  ,  , c, c ] // ...3 d's found, so...
st = [ 0, 2 ]                            // ...i = st.pop() - 1


              ->i               ->j      // i, j move up 1
S  = [ a, a, c, C<----------------C, c ] // S[j] overwrites S[i]
st = [ 0, 2 ]                            // S[i] == S[i-1], no change


                 ->i               ->j   // i, j move up 1
S  = [ a, a, c, c, C<----------------C ] // S[j] overwrites S[i]
st = [ 0, 2 ]                            // S[i] == S[i-1], no change
          i<--------                 j   // i moves back because...
S  = [ a, a, C--C--C,  ,  ,  ,  ,  ,   ] // ...3 c's found, so...
st = [ 0 ]                               // ...i = st.pop() - 1


S  = [ a, a ]                            // only keep S up to i
   = "aa"                                // then join to a string