Find whether an array is subset of another array using Map - GeeksforGeeks

08 Jun, 2021
Given two arrays: arr1[0..m-1] and arr2[0..n-1]. Find whether arr2[] is a subset of arr1[] or not. Both the arrays are not in sorted order. It may be assumed that elements in both arrays are distinct.Examples:  
Input: arr1[] = {11, 1, 13, 21, 3, 7},  arr2[] = {11, 3, 7, 1}
Output: arr2[] is a subset of arr1[]

Input: arr1[] = {1, 2, 3, 4, 5, 6},  arr2[] = {1, 2, 4}
Output: arr2[] is a subset of arr1[]

Input: arr1[] = {10, 5, 2, 23, 19},  arr2[] = {19, 5, 3}
Output: arr2[] is not a subset of arr1[]
 
Simple Approach: A simple approach is to run two nested loops. The outer loop picks all the elements of B[] one by one. The inner loop linearly searches for the element picked by the outer loop in A[]. If all elements are found, then print Yes, else print No. You can check the solution here.Efficient Approach: Create a map to store the frequency of each distinct number present in A[]. Then we will check if each number of B[] is present in map or not. If present in the map, we will decrement the frequency value for that number by one and check for the next number. If map value for any number becomes zero, we will erase it from the map. If any number of B[] is not found in the map, we will set the flag value and break the loops and print No. Otherwise, we will print Yes. 
C++
Java
Python
C#
Javascript
// C++ program to check if an array is// subset of another array #include <bits/stdc++.h>using namespace std; // Function to check if an array is// subset of another array int isSubset(int a[], int b[], int m, int n){     // map to store the values of array a[]    map<int, int> mp1;     for (int i = 0; i < m; i++)        mp1[a[i]]++;     // flag value    int f = 0;     for (int i = 0; i < n; i++) {        // if b[i] is not present in map        // then array b[] can not be a        // subset of array a[]         if (mp1.find(b[i]) == mp1.end()) {            f = 1;            break;        }         // if if b[i] is present in map        // decrement by one        else {            mp1[b[i]]--;             if (mp1[b[i]] == 0)                mp1.erase(mp1.find(b[i]));        }    }     return f;} // Driver codeint main(){    int arr1[] = { 11, 1, 13, 21, 3, 7 };    int arr2[] = { 11, 3, 7, 1 };     int m = sizeof(arr1) / sizeof(arr1[0]);    int n = sizeof(arr2) / sizeof(arr2[0]);     if (!isSubset(arr1, arr2, m, n))        cout<<"arr2[] is subset of arr1[] ";    else        cout<<"arr2[] is not a subset of arr1[]";     return 0;}
// Java program to check if an array is// subset of another arrayimport java.util.*; class GFG{     // Function to check if an array is    // subset of another array    static int isSubset(int a[], int b[], int m, int n)    {         // map to store the values of array a[]        HashMap<Integer, Integer> mp1 = new                HashMap<Integer, Integer>();         for (int i = 0; i < m; i++)            if (mp1.containsKey(a[i]))            {                mp1.put(a[i], mp1.get(a[i]) + 1);            }            else            {                mp1.put(a[i], 1);            }         // flag value        int f = 0;         for (int i = 0; i < n; i++)        {            // if b[i] is not present in map            // then array b[] can not be a            // subset of array a[]            if (!mp1.containsKey(b[i]))            {                f = 1;                break;            }             // if if b[i] is present in map            // decrement by one            else            {                mp1.put(b[i], mp1.get(b[i]) - 1);                 if (mp1.get(b[i]) == 0)                    mp1.remove(b[i]);            }        }         return f;    }     // Driver code    public static void main(String[] args)    {        int arr1[] = { 11, 1, 13, 21, 3, 7 };        int arr2[] = { 11, 3, 7, 1 };         int m = arr1.length;        int n = arr2.length;         if (isSubset(arr1, arr2, m, n)!=1)            System.out.print("arr2[] is subset of arr1[] ");        else            System.out.print("arr2[] is not a subset of arr1[]");    }} // This code is contributed by Rajput-Ji
# Python program to check if an array is# subset of another array # Function to check if an array is# subset of another arraydef isSubset(a, b, m, n) :         # map to store the values of array a    mp1 = {}    for i in range(m):        if a[i] not in mp1:            mp1[a[i]] = 0        mp1[a[i]] += 1         # flag value    f = 0    for i in range(n):                 # if b[i] is not present in map        # then array b can not be a        # subset of array a        if b[i] not in mp1:            f = 1            break                 # if if b[i] is present in map        # decrement by one        else :            mp1[b[i]] -= 1                         if (mp1[b[i]] == 0):                mp1.pop(b[i])    return f     # Driver codearr1 = [11, 1, 13, 21, 3, 7 ]arr2 = [11, 3, 7, 1 ] m = len(arr1)n = len(arr2) if (not isSubset(arr1, arr2, m, n)):    print("arr2[] is subset of arr1[] ")else:    print("arr2[] is not a subset of arr1[]") # This code is contributed by Shubhamsingh10
// C# program to check if an array is// subset of another arrayusing System;using System.Collections.Generic; class GFG{     // Function to check if an array is    // subset of another array    static int isSubset(int []a, int []b, int m, int n)    {         // map to store the values of array []a        Dictionary<int, int> mp1 = new                Dictionary<int, int>();         for (int i = 0; i < m; i++)            if (mp1.ContainsKey(a[i]))            {                mp1[a[i]] = mp1[a[i]] + 1;            }            else            {                mp1.Add(a[i], 1);            }         // flag value        int f = 0;         for (int i = 0; i < n; i++)        {            // if b[i] is not present in map            // then array []b can not be a            // subset of array []a            if (!mp1.ContainsKey(b[i]))            {                f = 1;                break;            }             // if if b[i] is present in map            // decrement by one            else            {                mp1[b[i]] = mp1[b[i]] - 1;                 if (mp1[b[i]] == 0)                    mp1.Remove(b[i]);            }        }         return f;    }     // Driver code    public static void Main(String[] args)    {        int []arr1 = {11, 1, 13, 21, 3, 7};        int []arr2 = {11, 3, 7, 1};         int m = arr1.Length;        int n = arr2.Length;         if (isSubset(arr1, arr2, m, n) != 1)            Console.Write("arr2[] is subset of arr1[] ");        else            Console.Write("arr2[] is not a subset of arr1[]");    }} // This code is contributed by PrinciRaj1992
<script> // JavaScript program to check if an array is// subset of another array // Function to check if an array is// subset of another array function isSubset(a, b, m, n) {     // map to store the values of array a[]    let mp = new Map();     for (let i = 0; i < m; i++) {         if (mp.has(a[i])) {            mp.set(a[i], mp.get(a[i]) + 1)        } else {            mp.set(a[i], 1)        }    }     // flag value    let f = 0;     for (let i = 0; i < n; i++) {        // if b[i] is not present in map        // then array b[] can not be a        // subset of array a[]         if (!mp.has(b[i])) {            f = 1;            break;        }         // if if b[i] is present in map        // decrement by one        else {            mp.set(b[i], mp.get(b[i]) - 1);             if (mp.get(b[i]) == 0)                mp.delete(b[i]);        }    }     return f;} // Driver code let arr1 = [11, 1, 13, 21, 3, 7];let arr2 = [11, 3, 7, 1]; let m = arr1.length;let n = arr2.length; if (!isSubset(arr1, arr2, m, n))    document.write("arr2[] is subset of arr1[] ");else    document.write("arr2[] is not a subset of arr1[]");  // This code is contributed by gfgking </script>
arr2[] is subset of arr1[]
 
Time Complexity: O (n) 
Rajput-Ji
princiraj1992
SHUBHAMSINGH10
gfgking
cpp-map
subset
Arrays
Arrays
subset
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