常见算法

var str = "abcdffffggj";
var obj = {};
for(var i = 0; i < str.length; i++){
　　//charAt() 方法可返回指定位置的字符。
    if(!obj[str.charAt(i)]){
       obj[str.charAt(i)] = 1; 
    }else{
        obj[str.charAt(i)]++;
    }
}
console.log(obj);

var max = 0, name = "";
for(var i in obj){
    if(obj[i] > max){
       max =  obj[i];
        name = i;
    }
}
console.log(name+":"+max);

var arr1 = [1,2,3];
var arr2 = [2,3,4,5,6];

let output = arr1
.filter(x => arr2.indexOf(x) == -1)
.concat(arr2.filter(x => arr1.indexOf(x) == -1));

console.log(output);

var arr = [];
for(var i = 0; i < 100; i++){
   arr[i]  = Math.floor(Math.random()*101);
}
console.log(arr);

var sorted = true;

for(var i = 0; i < arr.length; i++){
   for(var j = 0; j < arr.length - 1 - i; j++){
      if(arr[j] > arr[j+1]) {
         arr[j] = [arr[j+1],arr[j+1] = arr[j]][0];
         sorted=false;
      }
   }
    if(sorted==true){
            break;
     }        

}

function search(arr,data){
        var max = arr.length-1,  //最大值
            min = 0;  //最小值
        while(min<=max){
            var mid = Math.floor((max+min)/2); //中间值
            if(arr[mid]<data){
                min = mid+1;
            }else if(arr[mid]>data){
                max = mid-1;
            }else{
                return mid; 
            }
        }
        return -1;   //没找到返回-1
    }
      console.log(arr);//[0, 1, 2, 2, 3, 4, 4, 4, 5, 6, 7, 10, 11, 12, 14, 15, 16, 17, 18, 18, 20, 21, 23, 24, 24, 24, 25, 25, 25, 26, 28, 28, 34, 35, 35, 38, 39, 39, 40, 40, 42, 44, 48, 48, 49, 51, 51, 51, 53, 54, 54, 54, 55, 56, 58, 59, 59, 59, 60, 61, 62, 62, 63, 63, 65, 66, 67, 68, 68, 69, 69, 71, 71, 72, 73, 74, 76, 76, 77, 82, 83, 84, 85, 86, 86, 86, 86, 87, 90, 91, 91, 94, 94, 94, 94, 95, 95, 97, 98, 100]
　    console.log(search(arr,25)); //27
      console.log(search(arr,104));  //-1

function count(arr,data){
        var count = 0;
        var position = search(arr,data);
        if(position>-1){
            count++;
            for(var i=position-1;i>0;i--){
                if(arr[i]==data){
                    count++;
                }else{
                    break;
                }
            }
            for(var i=position+1;i<arr.length;i++){
                if(arr[i]==data){
                    count++;
                }else{
                    break;
                }
            }
        }
        return count;
    }