Permutation Sequence

Author: mengli

PermutationSequence.java

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+/**
+ * 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.
+ *
+ */
+
+public class PermutationSequence {
+	public String getPermutation(int n, int k) {
+		char[] arr = new char[n];
+		int pro = 1;
+		for (int i = 0; i < n; ++i) {
+			arr[i] = (char) ('1' + i);
+			pro *= (i + 1);
+		}
+		k = k - 1;
+		k %= pro;
+		pro /= n;
+		for (int i = 0; i < n - 1; ++i) {
+			int selectI = k / pro;
+			k = k % pro;
+			pro /= (n - i - 1);
+			int temp = arr[selectI + i];
+			for (int j = selectI; j > 0; --j) {
+				arr[i + j] = arr[i + j - 1];
+			}
+			arr[i] = (char) temp;
+		}
+		return String.valueOf(arr);
+	}
+}