[LeetCode 26] Remove Duplicates

Given a sorted array nums, 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 by modifying the input array in-place with O(1) extra memory.

Example 1:

Given *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 returned length.</pre>

Example 2:

Given *nums* = **[0,0,1,1,1,2,2,3,3,4]**,

Your function should return length = **`5`**, with the first five elements of *`nums`* being modified to **`0`**, **`1`**, **`2`**, **`3`**, and **`4`** respectively.

It doesn't matter what values are set beyond the returned length.

Clarification:

Confused why the returned value is an integer but your answer is an array?

Note that the input array is passed in by reference, which means modification to the input array will be known to the caller as well.

Internally you can think of this:
nums is passed in by reference. (i.e., without making a copy)

int len = removeDuplicates(nums);

// any modification to **nums** in your function would be known by the caller.
// using the length returned by your function, it prints the first **len** elements.
for (int i = 0; i < len; i++) {
    print(nums[i]);
}</pre>

Solution

1. Delete 是最后一个需要

class Solution {
    public int removeDuplicates(int[] nums) {
        if (nums == null || nums.length == 0)
            return 0;
        
        int delete = 0;
        int len = nums.length;
        
        for (int i = 0; i < nums.length; i++) {
            if (i > 0 && nums[i] == nums[i - 1]) {
                delete ++;
                len --;
            } else if (i > 0 && nums[i] != nums[i - 1]) {
                nums[i - delete] = nums[i];
            }
        }
        
        return len;

        //solution 2 using head 
        // head is the head index of non duplicated array
        int head = 0;
        for (int index = 1; index < nums.length; index ++) {
            if (nums[head] != nums[index]) {
                head ++;
                nums[head] = nums[index];
            }
        }
        
        return head + 1;
    }
}