Create PermutationSequence.cpp

Week 3/PermutationSequence.cpp

@@ -0,0 +1,40 @@
+/*
+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 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.
+Given k will be between 1 and n! inclusive.
+Example 1:
+
+Input: n = 3, k = 3
+Output: "213"
+*/
+class Solution {
+public:
+string getPermutation(int n, int k) {
+  int fact[10];
+  fact[0]=fact[1]=1;
+  for(int i=2;i<10;i++)
+    fact[i]=i*fact[i-1];
+  string res="",set="123456789";
+  while(n>0){
+    int p=(k-1)/fact[n-1];
+    res+=set[p];
+    set.erase(set.begin()+p);
+    k=k-p*fact[n-1];
+    n--;
+  }
+  return res;
+}
+};