38 lines
801 B
C++
38 lines
801 B
C++
#include <cctype>
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#include <string>
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#include <vector>
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#include <tuple>
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#include "defs.h"
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std::string LC230927::decodeAtIndex(const std::string& s, int k) {
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std::tuple<int, int, unsigned long long> col[51];
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int level = 0;
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unsigned long long len = 0;
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int begin = 0, end = 0;
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for (char ch : s) {
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if (std::isalpha(ch)) {
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++len;
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++end;
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} else { // num
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col[level++] = {begin, ch ^ 0x30, len *= (ch ^ 0x30)};
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begin = end = end + 1;
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}
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if (len >= k)
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break;
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}
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if (begin < end)
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col[level++] = {begin, 1, len};
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int ck = k - 1;
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for (int i = level - 1; i >= 0; --i) {
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const auto prev_len = i ? std::get<2>(col[i - 1]) : 0ULL;
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const auto& [b, c_dup, cur_len] = col[i];
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ck %= (cur_len / c_dup);
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if (ck >= prev_len)
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return {s[ck - prev_len + b]};
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}
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return {s[ck]};
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}
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