ALGO: Write algorithm to print all possible string by placing spaces between characters ?

Question

For example : input string is "xyz".
output should be
- xy z
- x yz
- x y z

Answer 1

// C++ program to print permutations of a given string with spaces.

#include <iostream>
#include <cstring>
using namespace std;

/* Function recursively prints the strings having space pattern.
   i and j are indices in 'str[]' and 'buff[]' respectively */
void printPatternUtil(char str[], char buff[], int i, int j, int n)
{
    if (i==n)
    {
        buff[j] = '\0';
        cout << buff << endl;
        return;
    }

    // Either put the character
    buff[j] = str[i];
    printPatternUtil(str, buff, i+1, j+1, n);

    // Or put a space followed by next character
    buff[j] = ' ';
    buff[j+1] = str[i];

    printPatternUtil(str, buff, i+1, j+2, n);
}

// This function creates buf[] to store individual output string and uses
// printPatternUtil() to print all permutations.
void printPattern(char *str)
{
    int n = strlen(str);

    // Buffer to hold the string containing spaces
    char buf[2*n]; // 2n-1 characters and 1 string terminator

    // Copy the first character as it is, since it will be always
    // at first position
    buf[0] = str[0];

    printPatternUtil(str, buf, 1, 1, n);
}

// Driver program to test above functions
int main()
{
    char *str = "XYZ";
    printPattern(str);
    return 0;
}

Time Complexity: Since number of Gaps are n-1, there are total 2^(n-1) patters each having length ranging from n to 2n-1. Thus overall complexity would be O(n*(2^n)).