From 7c317607f45fdb1e280bc96455456730a1841180 Mon Sep 17 00:00:00 2001
From: Lam Haoyin <root@eatswap.org>
Date: Wed, 2 Mar 2022 22:20:46 +0800
Subject: [PATCH] add: 220302-CN [cpp]

---
 cpp/2203/220302-CN.cpp  | 104 ++++++++++++++++++++++++++++++++++++++++
 cpp/2203/CMakeLists.txt |   2 +-
 2 files changed, 105 insertions(+), 1 deletion(-)
 create mode 100644 cpp/2203/220302-CN.cpp

diff --git a/cpp/2203/220302-CN.cpp b/cpp/2203/220302-CN.cpp
new file mode 100644
index 0000000..dc28c8d
--- /dev/null
+++ b/cpp/2203/220302-CN.cpp
@@ -0,0 +1,104 @@
+#include <string>
+#include <iostream>
+
+class Solution {
+private:
+	static inline constexpr unsigned long long diffULL(unsigned long long x, unsigned long long y) {
+		return std::max(x, y) - std::min(x, y);
+	}
+
+	static inline constexpr unsigned long long gen1001(unsigned long long n) {
+		int digits = 1;
+		for (auto i = n; i > 9; i /= 10)
+			++digits;
+		unsigned long long ret = 1;
+		for (int i = 0; i < digits; ++i)
+			ret *= 10;
+		return ret + 1;
+	}
+
+	static inline constexpr unsigned long long gen999(unsigned long long n) {
+		int digits = 1;
+		for (auto i = n; i > 9; i /= 10)
+			++digits;
+		unsigned long long ret = 1;
+		for (int i = 1; i < digits; ++i)
+			ret *= 10;
+		return ret - 1;
+	}
+
+public:
+	static std::string nearestPalindromic(const std::string& n) {
+		auto nNum = std::stoull(n);
+		if (nNum <= 10)
+			return std::to_string(nNum - 1);
+		else if (nNum == 11)
+			return "9";
+		else if (nNum <= 16)
+			return "11";
+		else if (nNum <= 26)
+			return "22";
+
+		auto nLen = n.length();
+		if (nLen & 1) {
+			auto absMin = 0xFFFFFFFFFFFFFFFFULL;
+			std::string ans;
+			for (int i = -1; i <= 1; ++i) {
+				std::string prefix = n.substr(0, nLen >> 1);
+				std::string thisNumStr = prefix;
+				thisNumStr.push_back(std::isdigit(n[nLen >> 1] + i) ? (n[nLen >> 1] + i) : n[nLen >> 1]);
+				thisNumStr.insert(thisNumStr.end(), prefix.rbegin(), prefix.rend());
+				auto thisNum = std::stoull(thisNumStr);
+				if (thisNum == nNum)
+					continue;
+				if (diffULL(thisNum, nNum) < absMin || (diffULL(thisNum, nNum) == absMin && thisNum < std::stoull(ans))) {
+					absMin = diffULL(thisNum, nNum);
+					ans = thisNumStr;
+				}
+			}
+
+			auto retNum = std::stoull(ans);
+			if (!absMin || (gen1001(nNum) != nNum && (diffULL(gen1001(nNum), nNum) < absMin || (diffULL(gen1001(nNum), nNum) == absMin && gen1001(nNum) < retNum)))) {
+				absMin = diffULL(gen1001(nNum), nNum);
+				retNum = gen1001(nNum);
+			}
+
+			if (!absMin || (gen999(nNum) != nNum && (diffULL(gen999(nNum), nNum) < absMin || (diffULL(gen999(nNum), nNum) == absMin && gen999(nNum) < retNum)))) {
+				retNum = gen999(nNum);
+			}
+
+			return std::to_string(retNum);
+		} else {
+			auto prefixNum = std::stoull(n.substr(0, nLen >> 1)), absMin = 0xFFFFFFFFFFFFFFFFULL;
+			std::string ans;
+			for (int i = -1; i <= 1; ++i) {
+				auto thisPrefix = std::to_string(prefixNum + i);
+				auto thisNumStr = thisPrefix;
+				thisNumStr.insert(thisNumStr.end(), thisPrefix.rbegin(), thisPrefix.rend());
+				auto thisNum = std::stoull(thisNumStr);
+				if (thisNum == nNum)
+					continue;
+				if (diffULL(thisNum, nNum) < absMin || (diffULL(thisNum, nNum) == absMin && thisNum < std::stoull(ans))) {
+					absMin = diffULL(thisNum, nNum);
+					ans = thisNumStr;
+				}
+			}
+
+			auto retNum = std::stoull(ans);
+			if (!absMin || (gen1001(nNum) != nNum && (diffULL(gen1001(nNum), nNum) < absMin || (diffULL(gen1001(nNum), nNum) == absMin && gen1001(nNum) < retNum)))) {
+				absMin = diffULL(gen1001(nNum), nNum);
+				retNum = gen1001(nNum);
+			}
+
+			if (!absMin || (gen999(nNum) != nNum && (diffULL(gen999(nNum), nNum) < absMin || (diffULL(gen999(nNum), nNum) == absMin && gen999(nNum) < retNum)))) {
+				retNum = gen999(nNum);
+			}
+
+			return std::to_string(retNum);
+		}
+	}
+};
+
+int main() {
+	std::cout << Solution::nearestPalindromic("12389");
+}
diff --git a/cpp/2203/CMakeLists.txt b/cpp/2203/CMakeLists.txt
index 17c58fa..71f8484 100644
--- a/cpp/2203/CMakeLists.txt
+++ b/cpp/2203/CMakeLists.txt
@@ -3,4 +3,4 @@ PROJECT(2203)
 
 SET(CMAKE_CXX_STANDARD 23)
 
-ADD_EXECUTABLE(2203 220301.cpp)
+ADD_EXECUTABLE(2203 220302-CN.cpp)