Add the initial EN translation for C++ code (#1346)

en/codes/cpp/chapter_backtracking/permutations_ii.cpp

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+/**
+ * File: permutations_ii.cpp
+ * Created Time: 2023-04-24
+ * Author: krahets (krahets@163.com)
+ */
+
+#include "../utils/common.hpp"
+
+/* Backtracking algorithm: Permutation II */
+void backtrack(vector<int> &state, const vector<int> &choices, vector<bool> &selected, vector<vector<int>> &res) {
+    // When the state length equals the number of elements, record the solution
+    if (state.size() == choices.size()) {
+        res.push_back(state);
+        return;
+    }
+    // Traverse all choices
+    unordered_set<int> duplicated;
+    for (int i = 0; i < choices.size(); i++) {
+        int choice = choices[i];
+        // Pruning: do not allow repeated selection of elements and do not allow repeated selection of equal elements
+        if (!selected[i] && duplicated.find(choice) == duplicated.end()) {
+            // Attempt: make a choice, update the state
+            duplicated.emplace(choice); // Record selected element values
+            selected[i] = true;
+            state.push_back(choice);
+            // Proceed to the next round of selection
+            backtrack(state, choices, selected, res);
+            // Retract: undo the choice, restore to the previous state
+            selected[i] = false;
+            state.pop_back();
+        }
+    }
+}
+
+/* Permutation II */
+vector<vector<int>> permutationsII(vector<int> nums) {
+    vector<int> state;
+    vector<bool> selected(nums.size(), false);
+    vector<vector<int>> res;
+    backtrack(state, nums, selected, res);
+    return res;
+}
+
+/* Driver Code */
+int main() {
+    vector<int> nums = {1, 1, 2};
+
+    vector<vector<int>> res = permutationsII(nums);
+
+    cout << "Input array nums = ";
+    printVector(nums);
+    cout << "All permutations res = ";
+    printVectorMatrix(res);
+
+    return 0;
+}