Monday, January 4, 2016

Print Concatenation of Zig-Zag String in 'n' Rows - GeeksforGeeks

Print Concatenation of Zig-Zag String in 'n' Rows - GeeksforGeeks
Given a string and number of rows 'n'. Print the string formed by concatenating n rows when input string is written in row-wise Zig-Zag fashion.
```Input: str = "ABCDEFGH"
n = 2
Output: "ACEGBDFH"
Explanation: Let us write input string in Zig-Zag fashion
in 2 rows.
A   C   E   G
B   D   F   H
Now concatenate the two rows and ignore spaces
in every row. We get "ACEGBDFH"

Input: str = "GEEKSFORGEEKS"
n = 3
Output: GSGSEKFREKEOE
Explanation: Let us write input string in Zig-Zag fashion
in 3 rows.
G       S       G       S
E   K   F   R   E   K
E       O       E
Now concatenate the two rows and ignore spaces
in every row. We get "GSGSEKFREKEOE"```
```1) Create an array strings, arr[n]
2) Initialize direction as "down" and row as 0. The
direction indicates whether we need to move up or
down in rows.
3) Traverse the input string, do following for every
character.
a) Append current character to string of current row.
b) If row number is n-1, then change direction to 'up'
c) If row number is 0, then change direction to 'down'
d) If direction is 'down', do row++.  Else do row--.
4) One by one print all strings of arr[]. ```
`void` `printZigZagConcat(string str, ``int` `n)`
`{`
`    ``// Corner Case (Only one row)`
`    ``if` `(n == 1)`
`    ``{`
`        ``cout << str;      `
`        ``return``;`
`    ``}   `

`    ``// Find length of string`
`    ``int` `len = str.length();`

`    ``// Create an array of strings for all n rows`
`    ``string arr[n];`

`    ``// Initialize index for array of strings arr[]`
`    ``int` `row = 0;`
`    ``bool` `down; ``// True if we are moving down in rows, `
`               ``// else false`

`    ``// Travers through given string`
`    ``for` `(``int` `i = 0; i < len; ++i)`
`    ``{`
`        ``// append current character to current row`
`        ``arr[row].push_back(str[i]);`

`        ``// If last row is reached, change direction to 'up'`
`        ``if` `(row == n-1)`
`          ``down = ``false``;`

`        ``// If 1st row is reached, change direction to 'down'`
`        ``else` `if` `(row == 0)`
`          ``down = ``true``;`

`        ``// If direction is down, increment, else decrement`
`        ``(down)? (row++): (row--);`
`    ``}`

`    ``// Print concatenation of all rows`
`    ``for` `(``int` `i = 0; i < n; ++i)`
`        ``cout << arr[i];`
`}`