JS面试：找出数组中出现次数最多的元素及其次数

1.使用map存储对应的数据，key是数据，value是出现的次数

function GetArrayMost(arr){
    var arrMap = new Map();
    var key = arr[0],
        value = 1;
    arr.forEach((item, index) => {
      if (arrMap.get(item) !== undefined) {
        let num = arrMap.get(item);
        arrMap.set(item, ++num);
      } else {
        arrMap.set(item, 1);
      }
      if (arrMap.get(item) > value) {
        key = item;
        value = arrMap.get(item);
      }
    });
    return [key,value];
}

//测试
var arr = [1,2,3,4,5,6,7,1,12,3,3,3,3,3,3,3,3,3]
console.log(
  "次数最多的元素为:",
  GetArrayMost(arr)[0],
  ",次数为:",
  GetArrayMost(arr)[1]
);
//次数最多的元素为: 3 ,次数为: 10

2.有点问题

function GetArrayMost__reduce(arr){
    var obj = arr.reduce((p,n) => (p[n]++ || (p[n] = 1),
                        (p.max = p.max >= p[n]? p.max: p[n]),
                        (p.key = p.max >= p[n]? p.key: n),p),{});
    return obj;
}


console.log(
  "次数最多的元素为:",
  GetArrayMost__reduce(arr).key,
  ",次数为:",
  GetArrayMost__reduce(arr).max
);

3.

function GetArrayMost__reduce(arr) {
    var maxElement;
    var maxNum = 1;
  var obj = arr.reduce(
    (p, n) => {
        p[n]? p[n]++: p[n] = 1;
        if(p[n] > maxNum){
            maxElement = n;
            maxNum++;
        }
        return p;
    },
    {}
  );
  return [maxElement, maxNum];
}

console.log(GetArrayMost__reduce(arr));

console.log(
  "次数最多的元素为:",
  GetArrayMost__reduce(arr)[0],
  ",次数为:",
  GetArrayMost__reduce(arr)[1]
);