Remove Element

Problem Statement

Given an integer array nums and an integer val, remove all occurrences of val in nums in-place. The order of the elements may be changed.

Return k, the number of elements in nums which are not equal to val. The first k elements of nums must contain those elements; the rest does not matter.

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Input / Output

Input:  nums = [3,2,2,3], val = 3
Output: 2, nums = [2,2,_,_]

Input:  nums = [0,1,2,2,3,0,4,2], val = 2
Output: 5, nums = [0,1,4,0,3,_,_,_]   (any order of the first 5 is accepted)

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Constraints

0 ≤ nums.length ≤ 100
0 ≤ nums[i] ≤ 50
0 ≤ val ≤ 100

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Understanding the Problem

• Keep everything that is not val, packed at the front
• In-place → no second array
• Order may change → allows the swap-with-end trick

Edge Cases

• Empty array → k = 0
• Every element equals val → k = 0
• val not present → k = n