Grokking the Coding Interview: Patterns for Coding Questions
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Solution: Single Number
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Problem Statement

In a non-empty array of integers, every number appears twice except for one, find that single number.

Example 1:

Input: 1, 4, 2, 1, 3, 2, 3
Output: 4

Example 2:

Input: 7, 9, 7
Output: 9

Constraints:

  • 1 <= nums.length <= 3 * 10<sup>4</sup>
  • -3 * 10<sup>4</sup> <= nums[i] <= 3 * 10<sup>4</sup>
  • Each element in the array appears twice except for one element which appears only once.

Solution

One straight forward solution can be to use a HashMap kind of data structure and iterate through the input:

1

.....

.....

.....

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