<算法>基本排序算法

冒泡排序

最大值向後冒泡
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Array.prototype.bubblesSort = function () {
    for (let i  = 0; i < this.length - 1; i++){
    	// 減i有效減小輪次
        for (let j = 0; j < this.length - 1 - i; j++){
            if(this[j] > this[j + 1]){
                let temp = this[j];
                this[j] = this[j + 1];
                this[j + 1] = temp;
            }
        }
    }
};
const arr = [5,4,3,2,1,0];
arr.bubblesSort();
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選擇排序

最小值排第一位、第二小值排第二位。以此類推
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Array.prototype.selectionSort = function () {
        for (let i = 0; i < this.length - 1; i++) {
            let indexMin = i;
            for (let j = i; j < this.length; j++) {
                if (this[j] < this[indexMin]) {
                    indexMin = j;
                }
            }
           // 交換操做
            if (indexMin !== i){
                const temp = this[i];
                this[i] = this[indexMin];
                this[indexMin] = temp;
            }
        }

        console.log(this);
    };
    const arr = [5,2, 4, 3, 2, 1];
    arr.selectionSort();
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插入排序

從第二個數開始往前比、比它大就日後排
 
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Array.prototype.insertionSort = function () {
       for (let i = 1; i < this.length; i++){
           const temp = this[i];
           let j = i;
           while (j > 0){
               if (this[j - 1] > temp){
                   this[j] = this[j - 1];
               } else {
                   break;
               }
               j -= 1;
           }
           this[j] = temp;
       }
       console.log(this);
   };
   const arr = [5,4,3,2,1,0];
   arr.insertionSort();
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快速排序

分區而後排序、性能較好、能夠項目中使用
  
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Array.prototype.quickSort = function () {
       const rec = (arr) => {
           // 遞歸作好跳出條件
           if (arr.length === 1) {return arr}
           let left = [];
           let right = [];
           const mid = arr[0];
           for (let i = 1; i < arr.length; i++){
               if (arr[i] < mid){
                   left.push(arr[i])
               } else {
                   right.push(arr[i]);
               }
           }
           return [...rec(left), mid, ...rec(right)];
       };
       const res = rec(this);
       res.forEach((n,i) => {
           this[i] = n
       });
       console.log(this);
   };
   const arr = [2,4,5,3,1];
   arr.quickSort();
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