查找字符串中出现最多的字符

方法一：利用js的split和join方法

function foo(str){
    var max = 0;
    var char = []; // 存放出现次数最多的字符
    while(str){
        var head = str.charAt(0);
        var arr = str.split(head);
        var num = str.length - arr.join('').length;
        if(num > max){
            max = num;
            char.length = 0;
            char.push(head);
        }else if(num === max){
            char.push(head);
        }
        str = arr.join('');
    }
    return {maxNum:max,chars:char};

}

方法二：此处要用对象key查找而不是用下标遍历，前者时间是1后者是n

function foo(str){
    let result = [];
    for(let i = 0; i < str.length; i++){
        if(result[str[i]]){
            result[str[i]] += 1;
        }else{
            result.push(str[i]);
            result[str[i]] = 1;
        }
    }

    let max = 0;
    let char = [];
    for(let key in result){
        if(result[key] > max){
            char.length = 0;
            max = result[key];
            char.push(key);
        }else if(result[key] === max){
            char.push(key);
        }
    }

    retrun {maxNum:max,chars:char};

}