Add C++ solutions for leetcode 60.

Author: yanglr

cpp-leetcode/leetcode60-permutation-sequence_factorial.cpp

@@ -0,0 +1,43 @@
+#include<vector>
+#include<algorithm>
+#include<iostream>
+#include<string>
+#include<cstring> /* 含memset */
+using namespace std;
+
+class Solution {
+public:
+    string getPermutation(int n, int k) {
+        int f[n]; // 记录阶乘 n! 的结果
+        memset(f, 0, sizeof(f));
+        f[0] = 1;
+        for (int i = 1; i < n; i++)
+            f[i] = i*f[i-1];
+        vector<int> digits; /* 1 <= n <= 9 */
+        for (int i = 1; i <= n; i++)
+            digits.push_back(i);
+
+        k--; // 1-indexed -> 0-indexed
+        string res = "";
+        for (int i = n - 1; i >= 0; i--)
+        {
+            int index = k / f[i];
+            res.push_back(digits[index] + '0');            
+            digits.erase(digits.begin() + index);
+            k = k % f[i];
+        }
+        return res;
+    }
+};
+
+// Test
+int main()
+{
+    Solution sol;
+    int n = 4;
+    int k = 9;
+    auto res = sol.getPermutation(n, k);
+    cout << res << endl;
+    
+    return 0;
+}

cpp-leetcode/leetcode60-permutation-sequence_next_permutation1.cpp

@@ -0,0 +1,30 @@
+#include<vector>
+#include<algorithm>
+#include<iostream>
+#include<string>
+using namespace std;
+
+class Solution {
+public:
+    string getPermutation(int n, int k) {
+        string s(n, '0');
+        
+        for (int i = 0; i < n; i++)
+            s[i] += i + 1;
+        for (int i = 0; i < k - 1; i++)
+            next_permutation(s.begin(), s.end());
+        return s;
+    }
+};
+
+// Test
+int main()
+{
+    Solution sol;
+    int n = 4;
+    int k = 9;
+    auto res = sol.getPermutation(n, k);
+    cout << res << endl;
+    
+    return 0;
+}

cpp-leetcode/leetcode60-permutation-sequence_next_permutation2.cpp

@@ -0,0 +1,30 @@
+#include<vector>
+#include<algorithm>
+#include<iostream>
+#include<string>
+using namespace std;
+
+class Solution {
+public:
+    string getPermutation(int n, int k) {
+        string res;
+        res.reserve(n);
+        for (int i = 1; i != n + 1; i++)
+            res.push_back(i + '0');
+        while (--k)
+            next_permutation(res.begin(), res.end());
+        return res;
+    }
+};
+
+// Test
+int main()
+{
+    Solution sol;
+    int n = 4;
+    int k = 9;
+    auto res = sol.getPermutation(n, k);
+    cout << res << endl;
+    
+    return 0;
+}