POJ 1850 Code(组合数学)
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Code
Time Limit: 1000MS | Memory Limit: 30000K | |
Total Submissions: 8662 | Accepted: 4113 |
Description
Transmitting and memorizing information is a task that requires different coding systems for the best use of the available space. A well known system is that one where a number is associated to a character sequence. It is considered that the words are made
only of small characters of the English alphabet a,b,c, ..., z (26 characters). From all these words we consider only those whose letters are in lexigraphical order (each character is smaller than the next character).
The coding system works like this:
? The words are arranged in the increasing order of their length.
? The words with the same length are arranged in lexicographical order (the order from the dictionary).
? We codify these words by their numbering, starting with a, as follows:
a - 1
b - 2
...
z - 26
ab - 27
...
az - 51
bc - 52
...
vwxyz - 83681
...
Specify for a given word if it can be codified according to this coding system. For the affirmative case specify its code.
The coding system works like this:
? The words are arranged in the increasing order of their length.
? The words with the same length are arranged in lexicographical order (the order from the dictionary).
? We codify these words by their numbering, starting with a, as follows:
a - 1
b - 2
...
z - 26
ab - 27
...
az - 51
bc - 52
...
vwxyz - 83681
...
Specify for a given word if it can be codified according to this coding system. For the affirmative case specify its code.
Input
The only line contains a word. There are some constraints:
? The word is maximum 10 letters length
? The English alphabet has 26 characters.
? The word is maximum 10 letters length
? The English alphabet has 26 characters.
Output
The output will contain the code of the given word, or 0 if the word can not be codified.
Sample Input
bf
Sample Output
55
Source
题意:给一个字符串,求这个字符串排第几?换句话说输出某个str字符串在字典中的位置,因为字典是从a=1開始的,因此str的位置值就是
在str前面全部字符串的个数 +1规定输入的字符串必须是升序排列。不降序列是非法字符串
#include<iostream> #include<algorithm> #include<stdio.h> #include<string.h> #include<stdlib.h> using namespace std; int c[27][27] = {0}; void updata() { for(int i=0;i<=26;i++) { for(int j=0;j<=i;j++) { if(j == 0 || i == j) { c[i][j] = 1; } else { c[i][j] = c[i-1][j-1] + c[i-1][j]; } } } c[0][0] = 0; } int main() { char str[20]; updata(); while(scanf("%s",str)!=EOF) { int len = strlen(str); for(int i=0;i<len-1;i++) { if(str[i]>=str[i+1]) { printf("0\n"); return 0; } } int sum = 0; for(int i=1;i<len;i++) { sum += c[26][i]; } for(int i=0;i<len;i++) { char ch = (i)?str[i-1]+1:‘a‘; while(ch<=str[i]-1) { sum += c[‘z‘-ch][len-1-i]; ch++; } } sum += 1; printf("%d\n",sum); } return 0; }
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