Naming a Company LeetCode solution in JavaScript

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/**
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 * @param {string[]} ideas
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 * @return {number}
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 */
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var distinctNames = function (ideas) {
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  let res = 0;
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  let lMap = new Map();
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  for (let i = 0; i < ideas.length; i++) {
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    let idea = ideas[i];
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    // extract first letter
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    let l = idea[0].charCodeAt() - 97;
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    // extract substring
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    let s = idea.substr(1);
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    // group substring by first letter
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    if (lMap.has(l)) {
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      // must use map not array
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      let m = lMap.get(l);
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      m.set(s, 1);
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      lMap.set(l, m);
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    } else {
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      let m = new Map();
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      m.set(s, 1);
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      lMap.set(l, m);
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    }
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  }
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  for (let i = 1; i < 26; i++) {
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    for (let j = 0; j < i; j++) {
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      // count substring with different first letter
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      let m = 0;
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      let m1 = lMap.has(i) ? lMap.get(i) : new Map();
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      let m2 = lMap.has(j) ? lMap.get(j) : new Map();
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      // both map must exist
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      if (m1.size > 0 && m2.size > 0) {
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        let k1 = Array.from(m1.keys());
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        for (let k = 0; k < k1.length; k++) {
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          if (m2.has(k1[k])) {
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            m++;
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          }
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        }
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        // the rest substring satisfy condition
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        res += (m1.size - m) * (m2.size - m);
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      }
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    }
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  }
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  // double for count A + B and B + A
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  res = res * 2;
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  return res;
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};