【LeetCode】26 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 nums = [1,1,2],

Your function should return length = 2, with the first two elements of nums being 1 and 2 respectively. It doesn’t matter what you leave beyond the new length.

Note:
The coperation on an Array is faster than on a Set.

Algorithm 1：（Runtime: 1 ms）

public class Solution {
    public int removeDuplicates(int[] nums) {
        int count = 0;
        int index = 1;
        for(int i = 0; i < nums.length - 1; i++){
            if(nums[i+1] == nums[i]){
                count++;
            }else{
                nums[index++] = nums[i+1];
            }
        }
        return nums.length - count;
    }
}

Algorithm 2：（Runtime: 6 ms）

public class Solution {
public int removeDuplicates(int[] nums) {
if(nums.length == 0){
return 0;
}
Set set = new HashSet();
int count = 0;
set.add(nums[0]);
int index = 1;
for(int i = 1; i < nums.length; i++){
if(!set.add(nums[i])){
count++;
}else{
nums[index++] = nums[i];
}
}
return nums.length - count;
}
}