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Added rotation string #1449

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Merged
realDuYuanChao merged 2 commits into from
Sep 8, 2020
Merged

Added rotation string #1449

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68bb2db
rotation string
realDuYuanChao Aug 30, 2020
c4a4b67
updating DIRECTORY.md
Sep 8, 2020
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1 change: 1 addition & 0 deletions DIRECTORY.md
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Original file line number Diff line number Diff line change
Expand Up @@ -241,4 +241,5 @@
* [Palindrome](https://github.com/TheAlgorithms/Java/blob/master/strings/Palindrome.java)
* [Pangram](https://github.com/TheAlgorithms/Java/blob/master/strings/Pangram.java)
* [ReverseString](https://github.com/TheAlgorithms/Java/blob/master/strings/ReverseString.java)
* [Rotation](https://github.com/TheAlgorithms/Java/blob/master/strings/Rotation.java)
* [Upper](https://github.com/TheAlgorithms/Java/blob/master/strings/Upper.java)
64 changes: 64 additions & 0 deletions strings/Rotation.java
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@@ -0,0 +1,64 @@
package strings;


/**
* Given a string, moving several characters
* in front of the string to the end of the string.
* For example, move the two characters'a' and 'b' in
* front of the string "abcdef" to the end of the string,
* so that the original string becomes the string "cdefab"
*/
public class Rotation {
public static void main(String[] args) {
assert rotation("abcdef", 2).equals("cdefab");

char[] values = "abcdef".toCharArray();
rotation(values, 2);
assert new String(values).equals("cdefab");
}

/**
* Move {@code n} characters in front of given string to the end of string
* time complexity: O(n)
* space complexity: O(n)
*
* @param s given string
* @param n the total characters to be moved
* @return string after rotation
*/
public static String rotation(String s, int n) {
return s.substring(n) + s.substring(0, n);
}

/**
* Move {@code n} characters in front of given character array to the end of array
* time complexity: O(n)
* space complexity: O(1)
*
* @param values given character array
* @param n the total characters to be moved
*/
public static void rotation(char[] values, int n) {
reverse(values, 0, n - 1);
reverse(values, n, values.length - 1);
reverse(values, 0, values.length - 1);
}

/**
* Reverse character array
*
* @param values character array
* @param from begin index of given array
* @param to end index of given array
*/
public static void reverse(char[] values, int from, int to) {
while (from < to) {
char temp = values[from];
values[from] = values[to];
values[to] = temp;
from++;
to--;
}
}

}