1
var countPalindromicSubsequence = function (s) {
2
  const charToIndices = {};
3
  for (let i = 0; i < s.length; i++) {
4
    const char = s[i];
5
    if (charToIndices[char]) {
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      charToIndices[char].push(i);
7
    } else {
8
      charToIndices[char] = [i];
9
    }
10
  }
11

12
  let count = 0;
13
  for (const currChar in charToIndices) {
14
    if (charToIndices[currChar].length < 2) continue;
15
    const currCharIndices = charToIndices[currChar];
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    const firstIndex = currCharIndices[0];
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    const lastIndex = currCharIndices[currCharIndices.length - 1];
18

19
    for (const char in charToIndices) {
20
      const indices = charToIndices[char];
21
      let lo = 0;
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      let hi = indices.length;
23
      while (lo < hi) {
24
        const mid = (lo + hi) >> 1;
25
        if (indices[mid] <= firstIndex) {
26
          lo = mid + 1;
27
        } else {
28
          hi = mid;
29
        }
30
      }
31
      if (indices[lo] && indices[lo] < lastIndex) {
32
        count++;
33
      }
34
    }
35
  }
36
  return count;
37
};