In this section we will see how to get all permutations of a string. The recursive approach is very simple. It uses the back-tracking procedure. But here we will use the iterative approach.
All permutations of a string ABC are like {ABC, ACB, BAC, BCA, CAB, CBA}. Let us see the algorithm to get the better idea.
Algorithm
getAllPerm(str)
begin sort the characters of the string while true, do print the string str i := length of str – 1 while str[i - 1] >= str[i], do i := i – 1 if i is 0, then return end if done j := length of str – 1 while j > i AND str[j] <= str[i – 1], do j := j – 1 done exchange the characters from position str[i - 1], str[j] reverse the string. done end
Example
#include <iostream>
#include <algorithm>
using namespace std;
void getAllPerm(string str){
sort(str.begin(), str.end());
while (true){
cout << str << endl;
int i = str.length() - 1;
while (str[i-1] >= str[i]){
if (--i == 0)
return;
}
int j = str.length() - 1;
while (j > i && str[j] <= str[i - 1])
j--;
swap(str[i - 1], str[j]);
reverse (str.begin() + i, str.end());
}
}
int main(){
string str = "WXYZ";
getAllPerm(str);
}Output
WXYZ WXZY WYXZ WYZX WZXY WZYX XWYZ XWZY XYWZ XYZW XZWY XZYW YWXZ YWZX YXWZ YXZW YZWX YZXW ZWXY ZWYX ZXWY ZXYW ZYWX ZYXW