[Leetcode 1] 26 Remove Duplicates from Sorted Array

Problem:

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]

 

Analysis: 

Use two pointers, ptrA always points to the last position of the no-dup array, ptrB traverse the original sorted array, once find an element not equal to *ptrA, increase ptrA and copy it to that position.

The time complexity is O(n) and the sapce complexity is O(n)

 

Code:

public class Solution {
    public int removeDuplicates(int[] A) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if (A.length == 0) return 0;
        
        int a = 0;
        for (int b=0; b<A.length; b++) {
            if (A[a] != A[b]) {
                A[++a] = A[b];
            }
        }
        
        return (a+1);
    }
}

 

Special Attention:

Pay attention to the special cases such as A is [], A is [1]