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01 First Duplicate

/**
 * 
 * Ashish Patel
 * e: ashishsushilPatel@gmail.com
 * w: https://ashish.me
 *
 */

/* 
 * Given an array a that contains only numbers in the range from 1 to a.length, find the first 
 * duplicate number for which the second occurrence has the minimal index. In other words, 
 * if there are more than 1 duplicated numbers, return the number for which the second occurrence 
 * has a smaller index than the second occurrence of the other number does. If there are no such 
 * elements, return -1.
 * 
 * Example
 * 
 * For a = [2, 1, 3, 5, 3, 2], the output should be firstDuplicate(a) = 3 
*/

function firstDuplicate(nums) {
  if(nums.length < 2) return -1;
  let lookupDict = {}
  for (let index = 0; index < nums.length; index++) {
    if(lookupDict[nums[index]]){
      return nums[index]
    } else {
      lookupDict[nums[index]] = 1
    }    
  }
  return -1
}

test('first Duplicate', () => {
  expect(firstDuplicate([2, 1, 3, 5, 3, 2])).toEqual(3)
});

Created 2020-03-26T12:35:28+00:00 · Edit