Create next-palindrome-using-same-digits.cpp

Author: kamyu104

C++/next-palindrome-using-same-digits.cpp

@@ -0,0 +1,46 @@
+// Time:  O(n)
+// Space: O(1)
+
+class Solution {
+public:
+    string nextPalindrome(string num) {
+        if (!nextPermutation(begin(num), begin(num) + size(num) / 2)) {
+            return "";
+        }
+        copy(begin(num), begin(num) + size(num) / 2, rbegin(num));
+        return num;
+    }
+
+private:
+    template<typename BidiIt>
+    bool nextPermutation(BidiIt begin, BidiIt end) {
+        const auto rbegin = reverse_iterator<BidiIt>(end);
+        const auto rend = reverse_iterator<BidiIt>(begin);
+        auto pivot = next(rbegin);
+        while (pivot != rend && *pivot >= *prev(pivot)) {
+            ++pivot;
+        }
+        bool is_greater = true;
+        if (pivot != rend) {
+            auto change = find_if(rbegin, pivot, bind1st(less<int>(), *pivot));
+            swap(*change, *pivot);
+        } else {
+            is_greater = false;
+        }        
+        reverse(rbegin, pivot);
+        return is_greater;
+    }
+};
+
+// Time:  O(n)
+// Space: O(1)
+class Solution2 {
+public:
+    string nextPalindrome(string num) {
+        if (!next_permutation(begin(num), begin(num) + size(num) / 2)) {
+            return "";
+        }
+        copy(begin(num), begin(num) + size(num) / 2, rbegin(num));
+        return num;
+    }
+};