# Interview Algorithms

Insights from Leetcode problems.

#### Finding a cycle in a linked-list

Use two runners.

Runner 1 goes two steps per iteration.

Runner 2 goes one step per iteration.

If there is a cycle, runner 2 will lap runner 1 within 2 cycles.

#### Finding duplicates in an array

If you have an array of ints where each number appears times and one number appears times where ,
then you count the number of times each bit appears and take it mod .

The remaining bits will remain times.