find-the-duplicate-number_0520.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>find-the-duplicate-number</title>
  </head>
  <body></body>
  <script>
    /**
     * @param {number[]} nums
     * @return {number}
     */
    var findDuplicate = function (nums) {
      let result = 0;
      const map = new Map();

      //set value and key in map
      for (num of nums) {
        map.set(num, map.get(num) + 1 || 1);
      }

      // check value
      map.forEach((value, key) => {
        if (value > 1) {
          result = key;
        }
      });

      return result;
    };
  </script>
</html>