### 056 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.
There are 2 duplicates: numbers 2 and 3. The second occurrence of 3 has a smaller index than the second occurrence of 2 does, so the answer is 3.

For a = [2, 4, 3, 5, 1], the output should be firstDuplicate(a) = -1.
*/

function firstDuplicate(array) {
const dupDict = {}
for (let index = 0; index < array.length; index++) {
const num = array[index]
if(dupDict.hasOwnProperty(num)){
return num
}
dupDict[num] = num

}
return -1
}

console.log(firstDuplicate([2, 1, 3, 5, 3, 2]))

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

Created 2019-12-16T23:51:57+05:30 · Edit