LeetCode – Permutation Sequence (Java)

The set [1,2,3,…,n] contains a total of n! unique permutations.

By listing and labeling all of the permutations in order,
We get the following sequence (ie, for n = 3):

"123"
"132"
"213"
"231"
"312"
"321"

Given n and k, return the kth permutation sequence. (Note: Given n will be between 1 and 9 inclusive.)

Java Solution 1

public class Solution {
	public String getPermutation(int n, int k) {
 
		// initialize all numbers
		ArrayList<Integer> numberList = new ArrayList<Integer>();
		for (int i = 1; i <= n; i++) {
			numberList.add(i);
		}
 
		// change k to be index
		k--;
 
		// set factorial of n
		int mod = 1;
		for (int i = 1; i <= n; i++) {
			mod = mod * i;
		}
 
		String result = "";
 
		// find sequence
		for (int i = 0; i < n; i++) {
			mod = mod / (n - i);
			// find the right number(curIndex) of
			int curIndex = k / mod;
			// update k
			k = k % mod;
 
			// get number according to curIndex
			result += numberList.get(curIndex);
			// remove from list
			numberList.remove(curIndex);
		}
 
		return result.toString();
	}
}

Java Solution 2

public class Solution {
	public String getPermutation(int n, int k) {
		boolean[] output = new boolean[n];
		StringBuilder buf = new StringBuilder("");
 
		int[] res = new int[n];
		res[0] = 1;
 
		for (int i = 1; i < n; i++)
			res[i] = res[i - 1] * i;
 
		for (int i = n - 1; i >= 0; i--) {
			int s = 1;
 
			while (k > res[i]) {
				s++;
				k = k - res[i];
			}
 
			for (int j = 0; j < n; j++) {
				if (j + 1 <= s && output[j]) {
					s++;
				}
			}
 
			output[s - 1] = true;
			buf.append(Integer.toString(s));
		}
 
		return buf.toString();
	}
}

Category >> Algorithms

If you want someone to read your code, please put the code inside <pre><code> and </code></pre> tags. For example:

<pre><code> 
String foo = "bar";
</code></pre>

Leo Rossignac-Milon

Sorry the post below is mine. This website, please step up your markdown game.

Here is an image of the working, short code:

http://tinypic.com/view.php?pic=1zvvkeu&s=8#.VCSh6CtdVFo
Guest

public static String kPerm (int n, int k){

ArrayList digits = new ArrayList();

for (int i=1; i<=n; i++) digits.add(i);

StringBuilder result = new StringBuilder();

for (int i=0; i=fac){

digitIndex++;

k-=fac;

}

result.append(digits.remove(digitIndex));

}

return result.toString();

}
Guest

public static String kPerm (int n, int k){
ArrayList digits = new ArrayList();
for (int i=1; i<=n; i++) digits.add(i);
StringBuilder result = new StringBuilder();

for (int i=0; i=fac){
digitIndex++;
k-=fac;
}

result.append(digits.remove(digitIndex));
}

return result.toString();
}
Guest

public static String kPerm (int n, int k){

ArrayList digits = new ArrayList();
for (int i=1; i<=n; i++) digits.add(i); //digits = 1,2,3,…,n
StringBuilder result = new StringBuilder();

for (int i=0; i=fac){
digitIndex++; //this digit must be the next largest available digit
k-=fac;
} //end while loop

result.append(digits.remove(digitIndex));
} //end for loop

return result.toString();
}
Leo Rossignac-Milon

I have a much simpler solution 🙂
kth permutation starts at 0

public static String kPerm (int n, int k){
….ArrayList digits = new ArrayList();
….for (int i=1; i<=n; i++) digits.add(i); //0,1,2,3,4….n
….StringBuilder result = new StringBuilder();

….for (int i=0; i=fac){ //we must shift to the next digit to the next largest available digit
…………….digitIndex++;
…………….k-=fac;
……..}
……..result.append(digits.remove(digitIndex));
….}
….return result.toString();
}
gk

The second solution is extremely hard to read. I saw a exact same one somewhere else.

LeetCode – Permutation Sequence (Java)

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