[POJ1496]Word Index
Word Index
| Time Limit: 1000MS | Memory Limit: 10000K | |
| Total Submissions: 3200 | Accepted: 1831 |
Description
Encoding
schemes are often used in situations requiring encryption or
information storage/transmission economy. Here, we develop a simple
encoding scheme that encodes particular types of words with five or
fewer (lower case) letters as integers.
Consider the English alphabet {a,b,c,...,z}. Using this alphabet, a set of valid words are to be formed that are in a strict lexicographic order. In this set of valid words, the successive letters of a word are in a strictly ascending order; that is, later letters in a valid word are always after previous letters with respect to their positions in the alphabet list {a,b,c,...,z}. For example,
abc aep gwz
are all valid three-letter words, whereas
aab are cat
are not.
For each valid word associate an integer which gives the position of the word in the alphabetized list of words. That is:
Your program is to read a series of input lines. Each input line will have a single word on it, that will be from one to five letters long. For each word read, if the word is invalid give the number 0. If the word read is valid, give the word's position index in the above alphabetical list.
Consider the English alphabet {a,b,c,...,z}. Using this alphabet, a set of valid words are to be formed that are in a strict lexicographic order. In this set of valid words, the successive letters of a word are in a strictly ascending order; that is, later letters in a valid word are always after previous letters with respect to their positions in the alphabet list {a,b,c,...,z}. For example,
abc aep gwz
are all valid three-letter words, whereas
aab are cat
are not.
For each valid word associate an integer which gives the position of the word in the alphabetized list of words. That is:
a -> 1
b -> 2
.
.
z -> 26
ab -> 27
ac -> 28
.
.
az -> 51
bc -> 52
.
.
vwxyz -> 83681
Your program is to read a series of input lines. Each input line will have a single word on it, that will be from one to five letters long. For each word read, if the word is invalid give the number 0. If the word read is valid, give the word's position index in the above alphabetical list.
Input
The
input consists of a series of single words, one per line. The words are
at least one letter long and no more that five letters. Only the lower
case alphabetic {a,b,...,z} characters will be used as input. The first
letter of a word will appear as the first character on an input line.
The input will be terminated by end-of-file.
The input will be terminated by end-of-file.
Output
The
output is a single integer, greater than or equal to zero (0) and less
than or equal 83681. The first digit of an output value should be the
first character on a line. There is one line of output for each input
line.
Sample Input
z
a
cat
vwxyz
Sample Output
26
1
0
83681
Source
我的解法：
先生成所有代码的字典，然后读入，再二分查找
const max=83681;
var s,s0:string;
s1:array[1..5] of char;
len,i,j:integer;
index,k:longint;
a:array[1..max] of string[5];
function valid(s:string):boolean;
var i:integer;
begin
for i:=2 to len do
if s[i]<=s[i-1] then exit(false);
exit(true);
end;
//生成字典
procedure find(t,l:integer);
var i:char;
begin
if t>l then
begin
inc(index);
s0:='';
for j:=1 to t-1 do
s0:=s0+s1[j];
a[index]:=s0;
exit;
end;
for i:='a' to 'z' do
if (t=1) or (i>s1[t-1]) then
begin
s1[t]:=i;
find(t+1,l);
end;
end;
//判定字符串s1不小于s2
function notsmall(s1,s2:string):boolean;
var i:integer;
begin
if (length(s1)>length(s2)) or ((length(s1)=length(s2)) and (s1>=s2)) then exit(true)
else exit(false);
end;
//二分法获取字符串index
function getIndex(s:string;l,r:longint):longint;
var i,k:longint;
begin
if l=r then exit(l)
else
begin
k:=(l+r) div 2;
if notsmall(a[k],s) then getIndex:=getIndex(s,l,k)
else getIndex:=getIndex(s,k+1,r);
end;
end;
begin
for i:=1 to 5 do
find(1,i);
while not EOF do
begin
readln(s);
len:=length(s);
if valid(s) then writeln(getIndex(s,1,max))
else writeln(0);
end;
end.
