D - Anagram POJ - 1256

Day3—D
You are to write a program that has to generate all possible words from a given set of letters.
Example: Given the word "abc", your program should - by exploring all different combination of the three letters - output the words "abc", "acb", "bac", "bca", "cab" and "cba".
In the word taken from the input file, some letters may appear more than once. For a given word, your program should not produce the same word more than once, and the words should be output in alphabetically ascending order.
Input
The input consists of several words. The first line contains a number giving the number of words to follow. Each following line contains one word. A word consists of uppercase or lowercase letters from A to Z. Uppercase and lowercase letters are to be considered different. The length of each word is less than 13.
Output
For each word in the input, the output should contain all different words that can be generated with the letters of the given word. The words generated from the same input word should be output in alphabetically ascending order. An upper case letter goes before the corresponding lower case letter.
Sample Input
3
aAb
abc
acba
Sample Output
Aab
Aba
aAb
abA
bAa
baA
abc
acb
bac
bca
cab
cba
aabc
aacb
abac
abca
acab
acba
baac
baca
bcaa
caab
caba
cbaa
Hint
An upper case letter goes before the corresponding lower case letter.
So the right order of letters is 'A'<'a'<'B'<'b'<...<'Z'<'z'.

题意：求全排列

思路：一开始不会，后来看了全排列以及相关函数，贴个链接吧，我也不太明白
http://www.360doc.com/content/17/0526/22/10408243_657563611.shtml

代码如下：

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>
#include<cmath>
using namespace std;
const int INF=0x3f3f3f3f;
bool cmp(char a,char b)
{
    if(tolower(a)!=tolower(b))
        return tolower(a)<tolower(b);    
    else
        return a<b;
}
int main()
{
    char s[20];
    int t;
    cin>>t;

    while(t--)
    {
        cin>>s;
        sort(s,s+strlen(s),cmp);  
        do
        {
            cout<<s<<endl;                            
        }while(next_permutation(s,s+strlen(s),cmp));  
    }
}