技術標籤：演算法與資料結構LeetCodeleetcode陣列雙指標

Topic

Array, Two Pointers

Description

https://leetcode.com/problems/remove-duplicates-from-sorted-array/

Given a sorted array nums, remove the duplicates in-place such that each element appears only once and returns 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.

Clarification:（講述呼叫函式，引數傳值而非傳引用，可忽略）

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 a 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]);
}

Example 1:

Input: nums = [1,1,2]
Output: 2, nums = [1,2]
Explanation: 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:

Input: nums = [0,0,1,1,1,2,2,3,3,4]
Output: 5, nums = [0,1,2,3,4]
Explanation: 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.

Constraints:

• 0 <= nums.length <= 3 * 10⁴
• -10⁴ <= nums[i] <= 10⁴
• nums is sorted in ascending order.

Analysis

用兩指標法，並利用陣列有序的屬性進行解答，注意兩指標下標的協調。

Submission

public class RemoveDuplicatesFromSortedArray {
	public int removeDuplicates(int[] nums) {
		int result = 0;

		if (nums.length > 0) {
			for (int i = result + 1; i < nums.length; i++) {
				if (nums[result] != nums[i]) {
					nums[++result] = nums[i];
				}
			}
			result++;
		}

		return result;
	}
}

Test

import static org.junit.Assert.*;

import java.util.Arrays;

import org.junit.Test;

public class RemoveDuplicatesFromSortedArrayTest {

	@Test
	public void test() {
		RemoveDuplicatesFromSortedArray obj = new RemoveDuplicatesFromSortedArray();

		int[] array = {0,0,1,1,1,2,2,3,3,4};
		int expectNum = 5;
		assertEquals(expectNum, obj.removeDuplicates(array));
		assertArrayEquals(new int[] {0,1,2,3,4}, Arrays.copyOfRange(array, 0, expectNum));
	}
}