LeetCode OJ:Remove Duplicates from Sorted Array II

Remove Duplicates from Sorted Array II

 

Follow up for "Remove Duplicates":
What if duplicates are allowed at most twice?

For example,
Given sorted array A = [1,1,1,2,2,3],

Your function should return length = 5, and A is now [1,1,2,2,3].

算法思想：

数组循环前移会超时，所以利用一辅助数组B去除不需要的元素，时间复杂度度O(n)，空间复杂度O(n)

class Solution {
public:
    int removeDuplicates(int A[], int n) {
        if(n<=2)return n;
        vector<bool> B(n,false);
        for(int i=1;i<n-1;i++)
            if(A[i]==A[i-1]&&A[i]==A[i+1])
                B[i+1]=true;
        int count=0;
        for(int i=0;i<n;i++)
            if(!B[i])A[count++]=A[i];
        return count;
    }
};

answer2

时间复杂度O(n)，空间复杂度O(1)

class Solution {
public:
    int removeDuplicates(int A[], int n) {
        if(n<=2)return n;
        
        int index=2;
        for(int i=2;i<n;++i){
            if(A[i]!=A[index-2])
                A[index++]=A[i];
        }
        return index;
    }
};

answer3

时间复杂度O(n)，空间复杂度O(1)

class Solution {
public:
    int removeDuplicates(int A[], int n) {
        if(n<=2)return n;
        
        int index=0;
        for(int i=0;i<n;i++){
            if(i>0&&i<n-1&&A[i]==A[i-1]&&A[i]==A[i+1])
                continue;
            A[index++]=A[i];
        }
        return index;
    }
};