[Leetcode] Remove Duplicates from Sorted Array II

题目：

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].

思路：双指针，设置一个flag，可以重复一次。

class Solution {public:    int removeDuplicates(int A[], int n) {        if (n <= 0) return n;        int runner = 0;        bool allow_dup = true;        for (int i = 1; i < n; ++i) {            if (A[i] == A[runner]) {                if (allow_dup) {                    A[++runner] = A[i];                    allow_dup = false;                }            } else {                allow_dup = true;                A[++runner] = A[i];            }        }        return runner + 1;    }};

总结：复杂度为O(n).