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2262.cpp
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2262.cpp
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class Solution {
public:
long long appealSum(string s) {
long long res = 0;
int n = s.size();
vector<vector<int>> indices(26, vector<int>(1, -1));
// collect index of each alphabet in s
for (int i = 0; i < n; i++) {
indices[s[i] - 'a'].push_back(i);
}
// for each alphabet
for (int i = 0; i < 26; i++) {
// if there is no such alphabet in the s, pass
if (indices[i].size() == 1) continue;
// for every two indices of that alphabet
for (int j = 1; j < indices[i].size(); j++) {
// calculate the combination
// e.g., abbca => [-1, 0, 4]
// 01234
// for [-1, 0] => (0 - (-1)) * (5 - 0) = 5 || a, ab, abb, abbc, abbca
// for [0, 4] => (4 - 0) * (5 - 4) = 4 || bbca, bca, ca, a
res += (indices[i][j] - indices[i][j - 1]) * (n - indices[i][j]);
}
}
return res;
}
};