function solution(A) {
    let arr = A.sort((a,b) => a-b);
    let length = A.length-1;
    if(A[0] !== 1) return 0;

    let ans = 1;
    for(let i = 0; i < length; i++){
        if(arr[i]+1 !== arr[i+1] && i !== length){
            ans = 0;
            break;
        }
    }
    return ans;
}