javascript union-find, using Map instead of Array. easy to understand:

function maxCircle(queries) {

let parentMap = new Map()
let sizeMap = new Map()
let maxGroup = 1


function find(p){
    if(parentMap.has(p)){
        while(p!==parentMap.get(p)){
            parentMap.set(p, parentMap.get(parentMap.get(p)))
            p = parentMap.get(p)
        }  
    }else{
        parentMap.set(p, p)   
    }

    return p
}

function union(p, q){
    let rootP = find(p)
    let rootQ = find(q)
    if(!sizeMap.has(rootP)){
        sizeMap.set(rootP, 1)
    }

    if(!sizeMap.has(rootQ)){
        sizeMap.set(rootQ, 1)
    }

    if(rootP===rootQ){
        return maxGroup
    }

    let groupSize = sizeMap.get(rootP)+sizeMap.get(rootQ)

    if(sizeMap.get(rootP)<sizeMap.get(rootQ)){
        parentMap.set(rootP, rootQ)
        sizeMap.set(rootQ, groupSize)  
    }else{
        parentMap.set(rootQ, rootP)
        sizeMap.set(rootP, groupSize)
    }
    maxGroup = Math.max(maxGroup, groupSize)
    return maxGroup
}

let res = []
for(let [p,q] of queries){
    res.push(union(p,q))
}

return res

}