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Author: assassint2017

Permutation Sequence/Permutation_Sequence.cpp

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+// Runtime: 4 ms, faster than 69.49% of C++ online submissions for Permutation Sequence.
+// Memory Usage: 8.1 MB, less than 98.28% of C++ online submissions for Permutation Sequence.
+
+class Solution
+{
+public:
+	string getPermutation(int n, int k)
+	{
+		string res = "";
+		--k;
+
+		vector<char> candidate(n);
+		for (int i = 0; i < n; ++i)
+			candidate[i] = i + 1;
+
+		for (int i = 0; i < n - 1; ++i)
+		{
+			int fac = factorial(n - 1 - i);
+			int index = k / fac;
+
+			res += candidate[index] + '1' - 1;
+			k %= fac;
+
+			vector<char>::iterator iter = candidate.begin() + index;
+			candidate.erase(iter);
+		}
+		res += candidate[0] + '1' - 1;
+		return res;
+	}
+private:
+
+	// 计算阶乘的小函数
+	int factorial(int n)
+	{
+		int res = 1;
+		for (int i = 1; i <= n; ++i)
+			res *= i;
+		return res;
+	}
+};