"CF676C" Vasya and String (binary lookup, linear scan ruler)

Test instructions

Give a string of length n, with only the characters ' a ' and ' B '. A maximum of K characters can be changed, that is, ' a ' becomes ' B ' or ' B ' becomes ' a '.

Ask the length of the string with the longest consecutive same character after the change.

First of all, two-point search, good to write

1 varSArray[0..100000] ofLongint;2 ch:ansistring;3 N,k,i,l,r,mid,last,ans:longint;4 5 functionMax (x,y:longint): Longint;6 begin7  ifX>y Thenexit (x);8 exit (y);9 End;Ten  One begin AAssign (input,'1.in'); Reset (input); -Assign (output,'1.out'); Rewrite (output); - readln (n,k); the READLN (CH); -   fori:=1  toN Do -  begin -s[i]:=s[i-1]; +   ifch[i]='b'  ThenInc (S[i]); -  End; +ans:=0; A   fori:=1  toN Do at   begin -L:=i; R:=n; last:=i; -    whileL<=r Do -   begin -mid:= (l+r) >>1; -    ifs[mid]-s[i-1]<=k Then beginLast:=mid; L:=mid+1;End in     Elser:=mid-1; -   End; toAns:=max (ans,last-i+1); +  End; -Fillchar (s,sizeof (s),0); the   fori:=1  toN Do *  begin $s[i]:=s[i-1];Panax Notoginseng   ifch[i]='a'  ThenInc (S[i]); -  End; the   fori:=1  toN Do +   begin AL:=i; R:=n; last:=i; the    whileL<=r Do +   begin -mid:= (l+r) >>1; $    ifs[mid]-s[i-1]<=k Then beginLast:=mid; L:=mid+1;End $     Elser:=mid-1; -   End; -Ans:=max (ans,last-i+1); the  End; - writeln (ans);Wuyi//close (input); the//close (output); - End.

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Then a linear scan, ACM called the Ruler method, the machine room big God called the extension of the head contraction tail

L +1 after the cycle is due to the beginning of the next continuous interval, and the current continuous between the letter and the next paragraph must be different (obviously to find the longest consecutive same sequence)

1 varch:ansistring;2 N,k,ans,r,l,i,t:longint;3 4 functionMax (x,y:longint): Longint;5 begin6  ifX>y Thenexit (x);7 exit (y);8 End;9 Ten begin OneAssign (input,'1.in'); Reset (input); AAssign (output,'1.out'); Rewrite (output); - readln (n,k); - READLN (CH); thel:=1; r:=1; t:=0; -   fori:=1  toN Do -  begin -   ifch[i]='b'  Then +   begin -    ifT<k Then beginInc (T); Inc (R);End +     Else A     begin at       while(l<=n) and(ch[l]='a') DoInc (L); - Inc (L); - Inc (R); -     End; -   End -    ElseInc (R); inAns:=max (ans,r-l); -  End; tol:=1; r:=1; t:=0; +   fori:=1  toN Do -  begin the   ifch[i]='a'  Then *   begin $    ifT<k Then beginInc (T); Inc (R);EndPanax Notoginseng     Else -     begin the       while(l<=n) and(ch[l]='b') DoInc (L); + Inc (L); A Inc (R); the     End; +   End -    ElseInc (R); $Ans:=max (ans,r-l); $  End; - writeln (ans); -//close (input); the//close (output); - End.

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"CF676C" Vasya and String (binary lookup, linear scan ruler)