|
| 1 | +// Two pointer solution, time O(n) and space O(1) |
| 2 | +classSolution { |
| 3 | +funbackspaceCompare(s:String,t:String):Boolean { |
| 4 | + |
| 5 | +funnextValidChar(str:String,_index:Int):Int { |
| 6 | +var backspace=0 |
| 7 | +var index=_index |
| 8 | +while (index>=0) { |
| 9 | +if (backspace==0&& str[index]!='#') |
| 10 | +break |
| 11 | +elseif (str[index]=='#') |
| 12 | + backspace++ |
| 13 | +else |
| 14 | + backspace-- |
| 15 | + index-- |
| 16 | + } |
| 17 | + |
| 18 | +return index |
| 19 | + } |
| 20 | + |
| 21 | +var index_s= s.lastIndex |
| 22 | +var index_t= t.lastIndex |
| 23 | +while (index_s>=0|| index_t>=0) { |
| 24 | + index_s= nextValidChar(s, index_s) |
| 25 | + index_t= nextValidChar(t, index_t) |
| 26 | + |
| 27 | +val char_s=if (index_s>=0) s[index_s]else'?' |
| 28 | +val char_t=if (index_t>=0) t[index_t]else'?' |
| 29 | +if (char_s!= char_t) |
| 30 | +returnfalse |
| 31 | + index_s-- |
| 32 | + index_t-- |
| 33 | + } |
| 34 | + |
| 35 | +returntrue |
| 36 | + } |
| 37 | +} |
| 38 | + |
| 39 | +// Stack solution, time O(n) and space O(n) |
| 40 | +classSolution { |
| 41 | +funbackspaceCompare(s:String,t:String):Boolean { |
| 42 | +val s1=LinkedList<Char>() |
| 43 | +val s2=LinkedList<Char>() |
| 44 | + |
| 45 | +for (cin s) { |
| 46 | +if (c=='#') { |
| 47 | +if (s1.isNotEmpty()) |
| 48 | + s1.removeLast() |
| 49 | + }else { |
| 50 | + s1.addLast(c) |
| 51 | + } |
| 52 | + } |
| 53 | + |
| 54 | +for (cin t) { |
| 55 | +if (c=='#') { |
| 56 | +if (s2.isNotEmpty()) |
| 57 | + s2.removeLast() |
| 58 | + }else { |
| 59 | + s2.addLast(c) |
| 60 | + } |
| 61 | + } |
| 62 | + |
| 63 | +return s1.joinToString("")== s2.joinToString("") |
| 64 | + } |
| 65 | +} |
| 66 | + |
| 67 | +// Another style of two pointer solution, same idea, without calling methods, time O(n) and space O(1) |
| 68 | +classSolution { |
| 69 | +funbackspaceCompare(s:String,t:String):Boolean { |
| 70 | +var i= s.lastIndex |
| 71 | +var j= t.lastIndex |
| 72 | +var steps=0 |
| 73 | + |
| 74 | +while (true) { |
| 75 | + steps=0 |
| 76 | +while (i>=0&& (steps>0|| s[i]=='#')) { |
| 77 | + steps+=if (s[i]=='#')1else-1 |
| 78 | + i-- |
| 79 | + } |
| 80 | + |
| 81 | + steps=0 |
| 82 | +while (j>=0&& (steps>0|| t[j]=='#')) { |
| 83 | + steps+=if (t[j]=='#')1else-1 |
| 84 | + j-- |
| 85 | + } |
| 86 | + |
| 87 | +if (i>=0&& j>=0&& s[i]== t[j]) { |
| 88 | + i-- |
| 89 | + j-- |
| 90 | + }else { |
| 91 | +break |
| 92 | + } |
| 93 | + } |
| 94 | + |
| 95 | +return i==-1&& j==-1 |
| 96 | + } |
| 97 | +} |