[leetcode] Remove Duplicates from Sorted Array

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].

https://oj.leetcode.com/problems/remove-duplicates-from-sorted-array/

思路：双指针。指针i遍历，指针j指向下一个unique的位置。注意corner case。

 

public class Solution {
    public int removeDuplicates(int[] A) {
        if (A == null)
            return 0;
        if (A.length < 1)
            return A.length;
        int n = A.length;
        int len = 1;
        for (int i = 1; i < n; i++) {
            if (A[i] != A[i - 1])
                A[len++] = A[i];
        }

        return len;

    }

    public static void main(String[] args) {
        System.out.println(new Solution().removeDuplicates(new int[] { 1, 1, 1, 2 }));
        System.out.println(new Solution().removeDuplicates(new int[] { 1, 1, 2, 2, 2, 2, 3, 3, 3, 4, 4, 5, 5 }));
        System.out.println(new Solution().removeDuplicates(new int[] {}));
        System.out.println(new Solution().removeDuplicates(new int[] { 1 }));
        System.out.println(new Solution().removeDuplicates(new int[] { 1, 1 }));
    }

}