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