111 lines
3.5 KiB
C++
111 lines
3.5 KiB
C++
#include <string>
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#include <iostream>
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/**
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* 564. Find the Closest Palindrome
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* Given a string n representing an integer, return the closest integer (not including itself), which is a palindrome. If there is a tie, return the smaller one.
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* The closest is defined as the absolute difference minimized between two integers.
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*/
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class Solution {
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private:
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static inline constexpr unsigned long long diffULL(unsigned long long x, unsigned long long y) {
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return std::max(x, y) - std::min(x, y);
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}
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static inline constexpr unsigned long long gen1001(unsigned long long n) {
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int digits = 1;
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for (auto i = n; i > 9; i /= 10)
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++digits;
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unsigned long long ret = 1;
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for (int i = 0; i < digits; ++i)
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ret *= 10;
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return ret + 1;
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}
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static inline constexpr unsigned long long gen999(unsigned long long n) {
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int digits = 1;
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for (auto i = n; i > 9; i /= 10)
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++digits;
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unsigned long long ret = 1;
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for (int i = 1; i < digits; ++i)
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ret *= 10;
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return ret - 1;
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}
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public:
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static std::string nearestPalindromic(const std::string& n) {
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auto nNum = std::stoull(n);
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if (nNum <= 10)
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return std::to_string(nNum - 1);
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else if (nNum == 11)
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return "9";
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else if (nNum <= 16)
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return "11";
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else if (nNum <= 26)
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return "22";
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auto nLen = n.length();
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if (nLen & 1) {
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auto absMin = 0xFFFFFFFFFFFFFFFFULL;
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std::string ans;
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for (int i = -1; i <= 1; ++i) {
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std::string prefix = n.substr(0, nLen >> 1);
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std::string thisNumStr = prefix;
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thisNumStr.push_back(std::isdigit(n[nLen >> 1] + i) ? (n[nLen >> 1] + i) : n[nLen >> 1]);
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thisNumStr.insert(thisNumStr.end(), prefix.rbegin(), prefix.rend());
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auto thisNum = std::stoull(thisNumStr);
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if (thisNum == nNum)
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continue;
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if (diffULL(thisNum, nNum) < absMin || (diffULL(thisNum, nNum) == absMin && thisNum < std::stoull(ans))) {
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absMin = diffULL(thisNum, nNum);
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ans = thisNumStr;
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}
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}
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auto retNum = std::stoull(ans);
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if (!absMin || (gen1001(nNum) != nNum && (diffULL(gen1001(nNum), nNum) < absMin || (diffULL(gen1001(nNum), nNum) == absMin && gen1001(nNum) < retNum)))) {
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absMin = diffULL(gen1001(nNum), nNum);
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retNum = gen1001(nNum);
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}
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if (!absMin || (gen999(nNum) != nNum && (diffULL(gen999(nNum), nNum) < absMin || (diffULL(gen999(nNum), nNum) == absMin && gen999(nNum) < retNum)))) {
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retNum = gen999(nNum);
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}
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return std::to_string(retNum);
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} else {
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auto prefixNum = std::stoull(n.substr(0, nLen >> 1)), absMin = 0xFFFFFFFFFFFFFFFFULL;
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std::string ans;
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for (int i = -1; i <= 1; ++i) {
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auto thisPrefix = std::to_string(prefixNum + i);
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auto thisNumStr = thisPrefix;
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thisNumStr.insert(thisNumStr.end(), thisPrefix.rbegin(), thisPrefix.rend());
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auto thisNum = std::stoull(thisNumStr);
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if (thisNum == nNum)
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continue;
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if (diffULL(thisNum, nNum) < absMin || (diffULL(thisNum, nNum) == absMin && thisNum < std::stoull(ans))) {
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absMin = diffULL(thisNum, nNum);
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ans = thisNumStr;
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}
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}
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auto retNum = std::stoull(ans);
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if (!absMin || (gen1001(nNum) != nNum && (diffULL(gen1001(nNum), nNum) < absMin || (diffULL(gen1001(nNum), nNum) == absMin && gen1001(nNum) < retNum)))) {
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absMin = diffULL(gen1001(nNum), nNum);
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retNum = gen1001(nNum);
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}
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if (!absMin || (gen999(nNum) != nNum && (diffULL(gen999(nNum), nNum) < absMin || (diffULL(gen999(nNum), nNum) == absMin && gen999(nNum) < retNum)))) {
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retNum = gen999(nNum);
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}
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return std::to_string(retNum);
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}
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}
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};
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int main() {
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std::cout << Solution::nearestPalindromic("12389");
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}
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