starfall124/length-longest-consecutive-elements-unsorted-array

length-longest-consecutive-elements-unsorted-array

Run this script

$ node index.js

All inputs are hard-coded in the following way:

/* index.js */

let nums = [100, 4, 200, 1, 3, 2];
console.log("Input = [" + nums + "]\n");
console.log("-----------------Result--------------------");
console.log("Output = " + longestConsecutiveLength(nums));
console.log("-------------------------------------------");

Steps to solve this problem

1. Return 0 if the given array is empty.

2. Declare five variables, map, max, start, end, and num, and set them {}, 0, 0, 0, and 0, respectively.

3. Use a for loop with index i and copy the value of the number with index i to the num.

4. Check if the num property of map object is defined or undefined.

5. If undefined, 5-1. If num - 1 property of map object is defined, assign map[num - 1].start to start else assign num to start.

   5-2. If num + 1 property of map object is defined, assign map[num + 1].end to end else assign num to end.

   5-3. Assign {start:num, end:num} to num property of map object.

   5-4. Assign end to map[start].end.

   5-5. Assign start to map[end].start.

   5-6. Assign max value of end - start + 1 and max to max

6. If defined, skip the current loop.

7. After the loop finishes, return the length of the longest consecutive elements array, which equals to max

Complexity:

• Time complexity of the above algorithm is O(n) because we are iterating over the input array only once and n is the total number of elements in that array.
• Constant space is O(n), because we are using extra space.