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#include <array>
#include <string>
using std::string;
class Solution {
public:
static int dfs(const std::string &s, int start, int end, int k) {
if (end - start < k) {
return 0;
}
std::array<int, 26> counts{0};
for (int i = start; i < end; i++) {
counts[s[i] - 'a']++;
}
int max = -1;
for (char c = 'a'; c <= 'z'; c++) {
int count = counts[c - 'a'];
if (count > 0 && count < k) {
int sub_start = start;
for (int i = start; i < end; i++) {
if (s[i] == c) {
if (sub_start != i) {
max = std::max(dfs(s, sub_start, i, k), max);
}
sub_start = i + 1;
}
}
if (sub_start != end) {
max = std::max(dfs(s, sub_start, end, k), max);
}
break; // This is vital.
}
}
if (max == -1)
return end - start;
else
return max;
}
int longestSubstring(string s, int k) { return dfs(s, 0, s.size(), k); }
};
int main() {
Solution{}.longestSubstring("aaaaaaaaaaaabcdefghijklmnopqrstuvwzyz", 3);
return 0;
}
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