Check if any two intervals intersects among a given set of intervals - GeeksforGeeks

24 Nov, 2021
An interval is represented as a combination of start time and end time. Given a set of intervals, check if any two intervals intersect. 
Examples: 
Input:  arr[] = {{1, 3}, {5, 7}, {2, 4}, {6, 8}}
Output: true
The intervals {1, 3} and {2, 4} overlap


Input:  arr[] = {{1, 3}, {7, 9}, {4, 6}, {10, 13}}
Output: false
No pair of intervals overlap. 
Expected time complexity is O(nLogn) where n is number of intervals.We strongly recommend to minimize your browser and try this yourself first.A Simple Solution is to consider every pair of intervals and check if the pair intersects or not. The time complexity of this solution is O(n2)
Method 1 A better solution is to Use Sorting. Following is complete algorithm. 1) Sort all intervals in increasing order of start time. This step takes O(nLogn) time. 2) In the sorted array, if start time of an interval is less than end of previous interval, then there is an overlap. This step takes O(n) time.So overall time complexity of the algorithm is O(nLogn) + O(n) which is O(nLogn).
Below is the implementation of above idea.
C++
Java
Javascript
// A C++ program to check if any two intervals overlap#include <algorithm>#include <iostream>using namespace std; // An interval has start time and end timestruct Interval {    int start;    int end;}; // Compares two intervals according to their starting time.// This is needed for sorting the intervals using library// function std::sort(). See http:// goo.gl/iGspVbool compareInterval(Interval i1, Interval i2){    return (i1.start < i2.start) ? true : false;} // Function to check if any two intervals overlapbool isIntersect(Interval arr[], int n){    // Sort intervals in increasing order of start time    sort(arr, arr + n , compareInterval);     // In the sorted array, if start time of an interval    // is less than end of previous interval, then there    // is an overlap    for (int i = 1; i < n; i++)        if (arr[i - 1].end > arr[i].start)            return true;     // If we reach here, then no overlap    return false;} // Driver programint main(){    Interval arr1[] = { { 1, 3 }, { 7, 9 }, { 4, 6 }, { 10, 13 } };    int n1 = sizeof(arr1) / sizeof(arr1[0]);    isIntersect(arr1, n1) ? cout << "Yes\n" : cout << "No\n";     Interval arr2[] = { { 6, 8 }, { 1, 3 }, { 2, 4 }, { 4, 7 } };    int n2 = sizeof(arr2) / sizeof(arr2[0]);    isIntersect(arr2, n2) ? cout << "Yes\n" : cout << "No\n";     return 0;}
// A Java program to check if any two intervals overlapimport java.io.*;import java.lang.*;import java.util.*; class GFG{ // An interval has start time and end timestatic class Interval{    int start;    int end;         public Interval(int start, int end)    {        super();        this.start = start;        this.end = end;    }}; // Function to check if any two intervals overlapstatic boolean isIntersect(Interval arr[], int n){     // Sort intervals in increasing order of start time    Arrays.sort(arr, (i1, i2) -> {        return i1.start - i2.start;    });     // In the sorted array, if start time of an interval    // is less than end of previous interval, then there    // is an overlap    for(int i = 1; i < n; i++)        if (arr[i - 1].end > arr[i].start)            return true;     // If we reach here, then no overlap    return false;} // Driver codepublic static void main(String[] args){    Interval arr1[] = { new Interval(1, 3),                        new Interval(7, 9),                        new Interval(4, 6),                        new Interval(10, 13) };    int n1 = arr1.length;     if (isIntersect(arr1, n1))        System.out.print("Yes\n");    else        System.out.print("No\n");     Interval arr2[] = { new Interval(6, 8),                        new Interval(1, 3),                        new Interval(2, 4),                        new Interval(4, 7) };    int n2 = arr2.length;         if (isIntersect(arr2, n2))        System.out.print("Yes\n");    else        System.out.print("No\n");}} // This code is contributed by Kingash
<script>// A Javascript program to check if any two intervals overlap // An interval has start time and end timeclass Interval{    constructor(start,end)    {        this.start = start;        this.end = end;    }} // Function to check if any two intervals overlapfunction isIntersect(arr,n){    // Sort intervals in increasing order of start time    arr.sort(function(i1, i2){        return i1.start - i2.start;    });      // In the sorted array, if start time of an interval    // is less than end of previous interval, then there    // is an overlap    for(let i = 1; i < n; i++)        if (arr[i - 1].end > arr[i].start)            return true;      // If we reach here, then no overlap    return false;} // Driver codelet arr1=[new Interval(1, 3),                        new Interval(7, 9),                        new Interval(4, 6),                        new Interval(10, 13) ];let n1 = arr1.length;if (isIntersect(arr1, n1))    document.write("Yes<br>");else    document.write("No<br>"); let arr2 = [ new Interval(6, 8),new Interval(1, 3),new Interval(2, 4),new Interval(4, 7) ];let n2 = arr2.length; if (isIntersect(arr2, n2))    document.write("Yes<br>");else    document.write("No<br>"); // This code is contributed by rag2127</script>
Output: 
No
Yes
Method 2: This approach is suggested by Anjali Agarwal. Following are the steps:  
1. Find the overall maximum element. Let it be max_ele 2. Initialize an array of size max_ele with 0. 3. For every interval [start, end], increment the value at index start, i.e. arr[start]++ and decrement the value at index (end + 1), i.e. arr[end + 1]- -. 4. Compute the prefix sum of this array (arr[]). 5. Every index, i of this prefix sum array will tell how many times i has occurred in all the intervals taken together. If this value is greater than 1, then it occurs in 2 or more intervals. 6. So, simply initialize the result variable as false and while traversing the prefix sum array, change the result variable to true whenever the value at that index is greater than 1.  
Below is the implementation of this (Method 2) approach. 
C++
Java
C#
Javascript
// A C++ program to check if any two intervals overlap#include <algorithm>#include <iostream>using namespace std; // An interval has start time and end timestruct Interval {    int start;    int end;}; // Function to check if any two intervals overlapbool isIntersect(Interval arr[], int n){     int max_ele = 0;     // Find the overall maximum element    for (int i = 0; i < n; i++) {        if (max_ele < arr[i].end)            max_ele = arr[i].end;    }     // Initialize an array of size max_ele    int aux[max_ele + 1] = { 0 };    for (int i = 0; i < n; i++) {         // starting point of the interval        int x = arr[i].start;         // end point of the interval        int y = arr[i].end;        aux[x]++, aux[y + 1]--;    }    for (int i = 1; i <= max_ele; i++) {        // Calculating the prefix Sum        aux[i] += aux[i - 1];         // Overlap        if (aux[i] > 1)            return true;    }     // If we reach here, then no Overlap    return false;} // Driver programint main(){    Interval arr1[] = { { 1, 3 }, { 7, 9 }, { 4, 6 }, { 10, 13 } };    int n1 = sizeof(arr1) / sizeof(arr1[0]);     isIntersect(arr1, n1) ? cout << "Yes\n" : cout << "No\n";     Interval arr2[] = { { 6, 8 }, { 1, 3 }, { 2, 4 }, { 4, 7 } };    int n2 = sizeof(arr2) / sizeof(arr2[0]);    isIntersect(arr2, n2) ? cout << "Yes\n" : cout << "No\n";     return 0;}// This Code is written by Anjali Agarwal
// A Java program to check if any two intervals overlapclass GFG{ // An interval has start time and end timestatic class Interval{    int start;    int end;    public Interval(int start, int end)    {        super();        this.start = start;        this.end = end;    }}; // Function to check if any two intervals overlapstatic boolean isIntersect(Interval arr[], int n){     int max_ele = 0;     // Find the overall maximum element    for (int i = 0; i < n; i++)    {        if (max_ele < arr[i].end)            max_ele = arr[i].end;    }     // Initialize an array of size max_ele    int []aux = new int[max_ele + 1];    for (int i = 0; i < n; i++)    {         // starting point of the interval        int x = arr[i].start;         // end point of the interval        int y = arr[i].end;        aux[x]++;        aux[y ]--;    }    for (int i = 1; i <= max_ele; i++)    {        // Calculating the prefix Sum        aux[i] += aux[i - 1];         // Overlap        if (aux[i] > 1)            return true;    }     // If we reach here, then no Overlap    return false;} // Driver programpublic static void main(String[] args){    Interval arr1[] = { new Interval(1, 3), new Interval(7, 9),                       new Interval(4, 6), new Interval(10, 13) };    int n1 = arr1.length;     if(isIntersect(arr1, n1))        System.out.print("Yes\n");    else        System.out.print("No\n");     Interval arr2[] = { new Interval(6, 8), new Interval(1, 3),                        new Interval(2, 4), new Interval(4, 7) };    int n2 = arr2.length;    if(isIntersect(arr2, n2))        System.out.print("Yes\n");    else        System.out.print("No\n");}} // This code is contributed by 29AjayKumar
// C# program to check if// any two intervals overlapusing System; class GFG{ // An interval has start time and end timeclass Interval{    public int start;    public int end;    public Interval(int start, int end)    {        this.start = start;        this.end = end;    }}; // Function to check if// any two intervals overlapstatic bool isIntersect(Interval []arr, int n){    int max_ele = 0;     // Find the overall maximum element    for (int i = 0; i < n; i++)    {        if (max_ele < arr[i].end)            max_ele = arr[i].end;    }     // Initialize an array of size max_ele    int []aux = new int[max_ele + 1];    for (int i = 0; i < n; i++)    {         // starting point of the interval        int x = arr[i].start;         // end point of the interval        int y = arr[i].end;        aux[x]++;        aux[y ]--;    }         for (int i = 1; i <= max_ele; i++)    {        // Calculating the prefix Sum        aux[i] += aux[i - 1];         // Overlap        if (aux[i] > 1)            return true;    }     // If we reach here, then no Overlap    return false;} // Driver Codepublic static void Main(String[] args){    Interval []arr1 = { new Interval(1, 3),                        new Interval(7, 9),                        new Interval(4, 6),                        new Interval(10, 13) };    int n1 = arr1.Length;     if(isIntersect(arr1, n1))        Console.Write("Yes\n");    else        Console.Write("No\n");     Interval []arr2 = { new Interval(6, 8),                        new Interval(1, 3),                        new Interval(2, 4),                        new Interval(4, 7) };    int n2 = arr2.Length;    if(isIntersect(arr2, n2))        Console.Write("Yes\n");    else        Console.Write("No\n");}} // This code is contributed by Rajput-Ji
<script>// A Javascript program to check if any two intervals overlap // An interval has start time and end timeclass Interval{    constructor(start, end)    {        this.start = start;        this.end = end;    }} // Function to check if any two intervals overlapfunction isIntersect(arr, n){    let max_ele = 0;      // Find the overall maximum element    for (let i = 0; i < n; i++)    {        if (max_ele < arr[i].end)            max_ele = arr[i].end;    }      // Initialize an array of size max_ele    let aux = new Array(max_ele + 1);    for(let i=0;i<(max_ele + 1);i++)    {        aux[i]=0;    }    for (let i = 0; i < n; i++)    {          // starting point of the interval        let x = arr[i].start;          // end point of the interval        let y = arr[i].end;        aux[x]++;        aux[y ]--;    }    for (let i = 1; i <= max_ele; i++)    {        // Calculating the prefix Sum        aux[i] += aux[i - 1];          // Overlap        if (aux[i] > 1)            return true;    }      // If we reach here, then no Overlap    return false;} // Driver programlet arr1 = [new Interval(1, 3), new Interval(7, 9),                       new Interval(4, 6), new Interval(10, 13)];let n1 = arr1.length;if(isIntersect(arr1, n1))        document.write("Yes<br>");    else        document.write("No<br>");      let arr2 = [ new Interval(6, 8), new Interval(1, 3),                        new Interval(2, 4), new Interval(4, 7) ];    let n2 = arr2.length;    if(isIntersect(arr2, n2))        document.write("Yes<br>");    else        document.write("No<br>"); // This code is contributed by avanitrachhadiya2155</script>
Output: 
No
Yes
Time Complexity : O(max_ele + n) 
Note: This method is more efficient than Method 1 if there are more number of intervals and at the same time maximum value among all intervals should be low, since time complexity is directly proportional to O(max_ele). Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above 
smitm1
Akanksha_Rai
29AjayKumar
Rajput-Ji
deepak_2431
Kingash
rag2127
avanitrachhadiya2155
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