Given a sorted array, remove the duplicates in place such that each element appear only once and return the new length.

Do not allocate extra space for another array, you must do this in place with constant memory.

For example,
Given input array A = [1,1,2],

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

class Solution {
public:
    int removeDuplicates(int A[], int n) {
        if (!n) return 0;
        int j = 0;
        for (int i=1; i<n; i++) {
                if (A[i-1] != A[i])
                        A[++j] = A[i];
        }
        return j+1;
    }
};

写法二：与唯一集合最后一个位置相比较

class Solution {
public:
    int removeDuplicates(int A[], int n) {
        if (!n) return 0;
        int j = 0;
        for (int i=1; i<n; i++) {
                if (A[j] != A[i])
                        A[++j] = A[i];
        }
        return j+1;
    }
};

Remove Duplicates from Sorted Array -- leetcode