js中常见算法

//1循环一次 
 var arr1 = [1,2,3,44,44,11,2,3,333,3,3];
    function removeRepeat(arr){
        var removeArr = [],obj = {};
        for(var i = 0, l = arr.length; i < l; i++){
            if(!obj[arr[i]]){
                removeArr.push(arr[i]);
                obj[arr[i]] = 1;
            }
        };
        return removeArr;
    }
    var singleArr = removeRepeat(arr1);
    console.log(singleArr); //[1, 2, 3, 44, 11, 333]

 function remove2(arr){
        return Array.from(new Set(arr));
    }
    var single2 = remove2(arr1);
    console.log(single2)  //[1, 2, 3, 44, 11, 333] es6 语法  其实问数组的去重主要是考上面一种思维方式

var str = "abbcccddddfffffgggggg";

    function maxNum(str){

        if(str.length <= 1){
            return str;
        }

        var a1 = str.split(‘‘),obj = {},result = [];
        //利用上面一个数组去重的思想
        for(var k = 0, l = a1.length; k < l; k++){
            if(!obj[a1[k]]){
                obj[a1[k]] = 1;
            }else {
                obj[a1[k]] += 1;
            };
        }

        var num = 0, word = "";
        for(var item in obj){
            if(obj[item] > num){
                num = obj[item];
                word = item;
            }
        }
        return word;
    }
    var w = maxNum(str);
    console.log(w);   //g

 var a3 = [1,4,2,90,3,4];

    for(var i = 0, l = a3.length; i < l - 1; i++){
        for(var j = i + 1; j < l; j++){
            if(a3[i] > a3[j]){
                var temp = a3[i];
                a3[i] = a3[j];
                a3[j] = temp;
            }
        }
    }
    console.log(a3);  //[1, 2, 3, 4, 4, 90]

var a3 = [1,4,2,90,3,4];
    for(var j = 0, l = a3.length; j < l; j++){
        for(k = l; k > j; k--){
            if(a3[j] > a3[k]){
                var temp = a3[j];
                a3[j] = a3[k];
                a3[k] = temp;
            }
        }
    }
    console.log(a3); ////[1, 2, 3, 4, 4, 90]  
    //跟冒泡排序的思维有点像，只是一直跟最后一个比，这样一轮下来，就排完序了。

 var a = 4,b = 5;
   function change(a,b) {
      b = b - a;
      a = a + b;
      b = a - b;
      return [a,b];   }
   console.log(change(a,b))    //思维方式不错。反正第一次的时候，没有想到 [5,4]