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100 Problems & Solutions Trang 57

Var st:string[10];
dem,M:longInt;
Begin
dem:=0;
M:=1;
Repeat
str(M,st);
dem := dem+length(st);
inc(M);
Until dem >= NN;
chuso := st[length(st) - (dem - NN)]
(*-------------------------------------*)
BEGIN
clrscr;;
write('Nhap k:');
Readln(k);
Writeln('Chu so thu', k,'cua day vo han cac so nguyen khong am');
write('123456789101112... la:', chu so(k));
Readln;
END.
Cách giải khác:
var n, Result: LongInt;

procedure ReadInput;
begin
Write('Ban hay nhap so K: '); Readln(n);
end;

procedure Solution;
var
i, Sum, Num, Digits: LongInt;
begin
Sum := 9; Num := 1; Digits := 1;
while Sum < n do
begin
Num := Num * 10; Inc(Digits);
Inc(Sum, Num * 9 * Digits);
end;
Dec(Sum, Num * 9 * Digits); Dec(n, Sum);
Num := Num + (n - 1) div Digits;
n := (n - 1) mod Digits + 1;
for i := 1 to Digits - n do Num := Num div 10;
Result := Num mod 10;
end;

procedure WriteOutput;
begin
Writeln('Chu so can tim la: ', Result);
Readln;
end;
begin

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