Given arrays a and b of size n and m respectively where m>=n. The task is to find the union between these two arrays and return the union array.

let a = [5, 3];
let b = [1, 2, 3, 4, 5];
let a = [2, 2];
let b = [1, 1];
let n = a.length;
let m = b.length;

for (let i = 0; i < m; i  ) {
  let present = true;
  
  for (let j = 0; j < n; j  ) {
    if (b[i] === a[j]) {
      present = false;
    }
  }
  
  if (present !== false) {
    a.push(b[i]);
  }
}

I am trying to solve this question from last 2 hour but I am not getting the desired output so please help me to solve this question.

CodePudding user response：

One way to do this is by taking advantage of the use of dictionaries in Javascript. Dictionaries are objects in Javascript, and they are used to store key-value pairs. The keys are unique, so if you add a key that already exists, it will overwrite the previous value. This is useful for finding the union of two arrays, because you can add all the elements of the first array to a dictionary, and then add all the elements of the second array to the dictionary. The dictionary will only contain unique elements, so the union of the two arrays will be the keys of the dictionary.

// Javascript code to find the union of two arrays
function array_union(arr1, arr2) {
    // Create a new dictionary
    var union = {};

    // Loop through the first array
    for (var i = 0; i < arr1.length; i  ) {
        // Add the element to the dictionary
        union[arr1[i]] = true;
    }

    // Loop through the second array
    for (var i = 0; i < arr2.length; i  ) {
        // Add the element to the dictionary
        union[arr2[i]] = true;
    }

    // Return the dictionary keys
    return Object.keys(union);
}

If you do not want to use dictionaries, you can use this naive approach:

function array_union(arr1, arr2) {
    // Create a new array
    var union = [];

    // Loop through the first array
    for (var i = 0; i < arr1.length; i  ) {
        // Check if the element is in the union array
        if (union.indexOf(arr1[i]) == -1) {
            // Add the element to the union array
            union.push(arr1[i]);
        }
    }

    // Loop through the second array
    for (var i = 0; i < arr2.length; i  ) {
        // Check if the element is in the union array
        if (union.indexOf(arr2[i]) == -1) {
            // Add the element to the union array
            union.push(arr2[i]);
        }
    }

    // Return the union array
    return union;
}

Finally, the "cool kids" way to do this is by using the reduce function. This is a very powerful function that can be used to perform a reduction on an array (checkout this explanation) . In this case, we are using it to create a new array where items are only added if they are not already in the array.

function array_union(n, m) {
    // Do a reduction on the two arrays to create a new array where items are only added if they are not already in the array
    let union = n.concat(m).reduce((a, b) => {
        if (a.indexOf(b) == -1) {
            a.push(b);
        }
        return a;
    }, []);
    
    return union;
}

CodePudding user response：

This is not the best solution I think but it is a start:

const union=(m,n)=>{
    let obj1={}
    let obj2={}
    let arr=[]
    for(let i=0;i<m.length;i  ){
        obj1[m[i]]=obj1[m[i]]?obj1[m[i]]  :1
        obj2[n[i]]=obj2[n[i]]?obj2[n[i]]  :1
    }
    for(let [key,value] of Object.entries(
        Object.keys(obj1).length>Object.keys(obj2).length?obj1:obj2
    )){
        if(obj1[key] && obj2[key]){
            arr.push(parseInt(key))
        }
    }
    return arr
}

 let a = [1,2,2,3];
 let b = [1,2,3,4,5];
 
console.log(union(a,b))