LeetCode 1213. Intersection of Three Sorted Arrays

原题链接在这里：https://leetcode.com/problems/intersection-of-three-sorted-arrays/

题目：

Given three integer arrays arr1, arr2 and arr3 sorted in strictly increasing order, return a sorted array of only the integers that appeared in all three arrays.

Example 1:

Input: arr1 = [1,2,3,4,5], arr2 = [1,2,5,7,9], arr3 = [1,3,4,5,8]
Output: [1,5]
Explanation: Only 1 and 5 appeared in the three arrays.

Constraints:

• 1 <= arr1.length, arr2.length, arr3.length <= 1000
• 1 <= arr1[i], arr2[i], arr3[i] <= 2000

题解：

Have 3 pointers pointing to 3 arrays.

If 3 pointed values are the same, add it to res and move all 3 pointers.

Else if first value < second value, move 1st pointer.

Else if second value < third value, now first value must be >= second value, need to move 2nd pointer.

Else move the 3rd pointer, since noew first value >= second value and second value >= third value.

Time Complexity: O(n). n = sum of array lengths.

Space: O(1).

AC Java:

class Solution {
    public List<Integer> arraysIntersection(int[] arr1, int[] arr2, int[] arr3) {
        List<Integer> res = new ArrayList<>();
        if(arr1 == null || arr2 == null || arr3 == null){
            return res;
        }
        
        int i = 0;
        int j = 0;
        int k = 0;
        while(i < arr1.length && j < arr2.length && k < arr3.length){
            if(arr1[i] == arr2[j] && arr1[i] == arr3[k]){
                res.add(arr1[i]);
                i++;
                j++;
                k++;
            }else if(arr1[i] < arr2[j]){
                i++;
            }else if(arr2[j] < arr3[k]){
                j++;
            }else{
                k++;
            }
        }
        
        return res;
    }
}

类似Intersection of Two Arrays.