26. Remove Duplicates from Sorted Array

题目描述：

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.
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]);
}

思路：设置两个指示器，左侧指示器pl和右侧指示器pr。pr从左往右移动，当pr所指的数值与pl所指数值不相同时，将pl右移一位，并将pr所指数值赋给pl。最后pl的大小即为修改后数组的长度。

参考代码：

#include <vector>
#include <iostream>
#include <assert.h>

using namespace std;


class Solution
{
 public:
  int removeDuplicates(vector<int>& nums)
  {
    if (nums.empty()) return 0;

    int index = 1;
    for (int i = 1; i < nums.size(); ++i)
    {
      if (nums[i] != nums[index - 1])
      {
        nums[index++] = nums[i];
//        nums[++index] = nums[i];    // logic error
      }
    }
    return index;
  }
};


int main()
{
    int a[] = {1, 1, 2, 2, 2, 3, 3, 4, 4, 4, 4};
    Solution solu;
    vector<int> vec_arr(a, a+11);
    int res_vec_len = solu.removeDuplicates(vec_arr);
    for (int i = 0; i < res_vec_len; ++i)
    {
        cout << vec_arr[i] << endl;
    }
    assert(res_vec_len != vec_arr.size());
    cout << res_vec_len << " " << vec_arr.size() << endl;

    return 0;
}

程序输出为：

1
2
3
4
4 11