[LeetCode] 26. Remove Duplicates from Sorted Array 有序数组中去除重复项

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:

2
nums
1
2

Example 2:

5
nums
0
1
2
3
4

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]);
}

去除有序数组中的重复项，返回新数组的长度，要求in-place，O(1)的额外空间。

解法：双指针Two Pointers，一个指针遍历数组所有元素，一个指针指向遍历后的不重复元素的边界。

Java:

class Solution {
    public static int removeDuplicatesNaive(int[] A) {
      if (A.length < 2)
        return A.length;
 
      int j = 0;
      int i = 1;
 
      while (i < A.length) {
        if (A[i] == A[j]) {
          i++;
        } else {
          j++;
          A[j] = A[i];
          i++;
        }
      }
 
      return j + 1;
    }
}

Python：

class Solution:
    # @param a list of integers
    # @return an integer
    def removeDuplicates(self, A):
        if not A:
            return 0
         
        last, i = 0, 1
        while i < len(A):
            if A[last] != A[i]:
                last += 1
                A[last] = A[i]
            i += 1
             
        return last + 1

C++:

class Solution {
public:
    int removeDuplicates(vector<int>& nums) {
        if (nums.empty()) return 0;
        int pre = 0, cur = 0, n = nums.size();
        while (cur < n) {
            if (nums[pre] == nums[cur]) ++cur;
            else nums[++pre] = nums[cur++];
        }
        return pre + 1;
    }
};

C++:

class Solution {
    public:
    int removeDuplicates(int A[], int n) {
        if(n < 2) return n;
        int id = 1;
        for(int i = 1; i < n; ++i) 
            if(A[i] != A[i-1]) A[id++] = A[i];
        return id;
    }
};