Zig-Zag Triangle – String Pattern

Print a zig-zag triangular pattern using characters from a string with alternating forward and reverse order

Understand the Problem

Problem Statement

Zig-Zag Triangle – String Pattern: The program must accept a string S and an integer N as the input. The program must print N lines of output based on the following conditions.

The 1^st line contains N-1 asterisks and the first character of S.
The 2^nd line contains N-2 asterisks and the next 3 characters of S.
The 3^rd line contains N-3 asterisks and the next 5 characters of S in reverse order.
The 4^th line contains N-4 asterisks and the next 7 characters of S.
The 5^th line contains N-5 asterisks and the next 9 characters of S in reverse order.
Similarly, the remaining lines are printed in the zig-zag order.
If there are no more characters in S when printing lines, the program must print # for those characters.

Constraints

1 ≤ Length of S ≤ 1000
3 ≤ N ≤ 50
Characters can be any printable ASCII characters
Output lines will have decreasing asterisks from N-1 to 0
Character extraction follows odd number sequence: 1, 3, 5, 7, 9...
Odd-numbered lines (1st, 3rd, 5th...) print characters in reverse order
Even-numbered lines (2nd, 4th, 6th...) print characters in normal order

Examples

Example 1

Input

skillrack
3

Output

**s
*kil
kcarl

Explanation

For N=3: - Line 1: 2 asterisks + 1st character 's' → '**s' - Line 2: 1 asterisk + next 3 characters 'kil' → '*kil' - Line 3: 0 asterisks + next 5 characters 'lrack' in reverse → 'kcarl'

Example 2

Input

Telegram
4

Output

***T
**ele
*#marg
#######

Explanation

For N=4: - Line 1: 3 asterisks + 1st character 'T' → '***T' - Line 2: 2 asterisks + next 3 characters 'ele' → '**ele' - Line 3: 1 asterisk + next 5 characters, but only 'gram' available, so padded with '#' → '*#marg' - Line 4: 0 asterisks + next 7 characters, all padded with '#' → '#######'

Example 3

Input

Acknowledgement
3

Output

**A
*ckn
delwo

Explanation

For N=3: - Line 1: 2 asterisks + 1st character 'A' → '**A' - Line 2: 1 asterisk + next 3 characters 'ckn' → '*ckn' - Line 3: 0 asterisks + next 5 characters 'delwo' in reverse → 'delwo'

Solution

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int main() {
    char s[10000];
    int n;
    
    // Read input
    fgets(s, sizeof(s), stdin);
    s[strcspn(s, "\n")] = 0; // Remove newline
    scanf("%d", &n);
    
    // Pad string with '#' characters
    int len = strlen(s);
    for (int i = len; i < 10000; i++) {
        s[i] = '#';
    }
    s[9999] = '\0';
    
    int index = 0;
    
    // Generate each line
    for (int line = 1; line <= n; line++) {
        // Print leading asterisks
        for (int j = 0; j < n - line; j++) {
            printf("*");
        }
        
        // Calculate number of characters to extract (1, 3, 5, 7...)
        int chars_to_extract = 2 * line - 1;
        
        // Extract characters
        char temp[100];
        for (int j = 0; j < chars_to_extract; j++) {
            temp[j] = s[index + j];
        }
        temp[chars_to_extract] = '\0';
        
        // Print in reverse order for odd-numbered lines
        if (line % 2 == 1) {
            for (int j = chars_to_extract - 1; j >= 0; j--) {
                printf("%c", temp[j]);
            }
        } else {
            printf("%s", temp);
        }
        
        printf("\n");
        index += chars_to_extract;
    }
    
    return 0;
}

Time:O(N²) - The outer loop runs N times, and the inner character processing can take up to O(N) time in the worst case.

Space:O(1) - Uses a fixed-size character array and minimal additional variables.

Approach:

The C solution follows these steps:

Input Reading: Uses fgets() to read the string and scanf() for the integer N.
String Padding: Extends the string with '#' characters to prevent index out-of-bounds errors during character extraction.
Line Generation Loop: Iterates from 1 to N to generate each line.
Asterisk Printing: Prints N-line asterisks at the beginning of each line.
Character Extraction: Calculates the number of characters to extract using the formula 2*line-1, which gives the sequence 1, 3, 5, 7...
Reverse Logic: For odd-numbered lines (line % 2 == 1), prints characters in reverse order. For even-numbered lines, prints in normal order.
Index Management: Advances the character index by the number of characters extracted for the next iteration.

The solution handles edge cases where the string runs out of characters by padding with '#' characters.

Visual Explanation

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