문제

Given an integer array nums sorted in non-decreasing order, remove some duplicates in-place such that each unique element appears at most twice. The relative order of the elements should be kept the same.

Since it is impossible to change the length of the array in some languages, you must instead have the result be placed in the first part of the array nums. More formally, if there are k elements after removing the duplicates, then the first k elements of nums should hold the final result. It does not matter what you leave beyond the first k elements.

Return k after placing the final result in the first k slots of nums.

Do not allocate extra space for another array. You must do this by modifying the input array in-place with O(1) extra memory.

구현 전 예상 풀이

의사코드

idx = 2;

for(i = 2; i < nums.length; i++)
	num1 = nums[idx - 2]
    num2 = nums[idx - 1]
    num3 = nums[i]
    
    if(num1 == num3 && num2 == num3)
    	continue
    
    nums[idx] = num3
    idx++
    
return idx

구현 코드

public int removeDuplicates(int[] nums) {
    int idx = 2;

    for (int i = 2; i < nums.length; i++) {
        int num1 = nums[idx - 2];
        int num2 = nums[idx - 1];
        int num3 = nums[i];

        if (num1 == num3 && num2 == num3) {
            continue;
        }

        nums[idx] = num3;
        idx++;
    }

    return idx;
}

결과

다른 사람 풀이

정렬 된 배열이라는 것을 활용하면 내 풀이보다 더 간단하게 작성 가능하다

public int removeDuplicates(int[] nums) {
   int i = 0;
   for (int n : nums)
      if (i < 2 || n > nums[i - 2])
         nums[i++] = n;
   return i;
}

80. Remove Duplicates from Sorted Array II
다른 사람 풀이 링크