# Find intersection between Two Sorted Arrays.

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

Examples:

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

Approach:

Naive Approach: Use 2 loops and compare each elements in both array 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 the arrays.(x=0, y=0)
• If both elements are same, we have our intersection point, return it.
• Else if element of arrA[x] > element of arrB[y], increase the arrB[] index, y++.
• Else if element of arrA[x] < element of arrB[y], increase the arrA[] index, x++.
• If any of the array gets over that means you have not found the intersection point. return -1.

Complete Code:

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 public class IntersecionPoint2Arrays { int intersectionPoint = –1; int x; int y; public int intersection(int[] arrA, int[] arrB) { while (x < arrA.length && y < arrB.length) { if (arrA[x] > arrB[y]) y++; else if (arrA[x] < arrB[y]) x++; else { intersectionPoint = arrA[x]; return intersectionPoint; } } return intersectionPoint; } public static void main(String[] args) throws java.lang.Exception { int[] a = { 1, 2, 3, 6, 8, 10 }; int[] b = { 4, 5, 6, 11, 15, 20 }; IntersecionPoint2Arrays i = new IntersecionPoint2Arrays(); System.out.println("Intersection point is : " + i.intersection(a, b)); } }

Output:

```Intersection point is : 6
```

### 4 thoughts on “Find intersection between Two Sorted Arrays.”

1. Dude this doesn’t work . Try this input

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

or this

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

I have modified this

package com.prasanth.groovy;

public class IntersecionPoint2Arrays {

int intersectionPoint = -1;
int x;
int y;

public int intersection(int[] arrA, int[] arrB) {
while (x < arrA.length) {

for(int z : arrB)
{
if (arrA[x] == z)
return intersectionPoint = arrA[x];

}
x++;

}
return -1;
}

public static void main(String[] args) throws java.lang.Exception {
int[] a = { 1, -2, 3, 6, 8, 10 };
int[] b = { 31, 30, 61, 11, 34, -2 };
IntersecionPoint2Arrays i = new IntersecionPoint2Arrays();
System.out.println("Intersection point is : " + i.intersection(a, b));

}
}

• Question says Sorted array. :/

2. ooh the precondition says the arrays are sorted .. Then I think the first case fails when both elements show up in the same place …

eg a = 6 and b = 6

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

• 