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87. Find Intersection of Two Sorted Arrays

Objective: Given two sorted arrays, Find the intersection points between them.


int[] a = { 1, 2, 3, 6, 8, 10 };
int[] b = { 4, 5, 6, 11, 15, 20 };
Output: Intersection point is : 6


Naive Approach: Use 2 loops and compare each element in both arrays and as soon as you find the intersection point, return it. Time Complexity - O(n2).

Better Approach: Time Complexity - O(n)

  • Say Arrays are arrA[] and arrB[] and indexes for navigation are x and y respectively.
  • Since arrays are sorted, compare the first element of both arrays. (x=0, y=0)
  • If both elements are the same, we have our intersection point and return it.
  • Else if arrA[x] > arrB[y], increase the arrB[] index, y++.
  • Else if arrA[x] < arrB[y], increase the arrA[] index, x++.
  • If any of the arrays gets over that means we have not found the intersection point. return -1.


Intersection point is : 6