几种排序

1. 选择排序

let sort = (numbers) =>{
    for(let i = 0; i < numbers.length -1; i++){
        console.log(`----`)
        console.log(`i: ${i}`)
        let index = minIndex(numbers.slice(i)) + i
        console.log(`index: ${index}`)
        console.log(`min: ${numbers[index]}`)
        if(index!==i){
            swap(numbers, index, i)
            console.log(`swap ${index}: ${i}`)
            console.log(numbers)
        }
        return numbers
    }
}
 let swap = (array, i, j) => {
     let temp = array[i]
     array[i] = array[j]
     array[j] = temp
 }
 let minIndex = (numbers) =>{
     let index = 0
     for(let i=0; i<numbers.length;i++){
         if(numbers[i] < numbers[index]){
             index = i
         }
     }
     return index
 }

浏览器运行： 2. 快速排序

let quickSort = arr =>{
    if (arr.length <= 1 ) { return arr; }
    let pivotIndex = Math.floor(arr.length / 2);
    let pivot = arr.splice(pivotIndex, 1)[0];
    let left = [];
    let right = [];
    for (let i = 0; i < arr.length;i++){
        if (arr[i] < pivot) { left.push(arr[i])
        } else { right.push(arr[i])
        }
        return quickSort(left).concat(
                 [pivot],quickSort(right)
            )
    }
}

3. 归并排序

let mergeSort = arr =>{
    let k = arr.length
    if (k === 1){return arr}
        let left = arr.slice(0, Math.floor(k/2))
        let right = arr.slice(Math.floor(k/2))
        return merge(mergeSort(left),mergeSort(right))
}
let merge = (a, b) =>{
    if(a.length === 0) return b
    if(b.length === 0) return a
    return a[0] > b[0] ?
      [b[0]].concat(merge(a, b.slice(1))):
      [a[0]].concat(merge(a.slice(1),b))
}

4. 计数排序

let countSort = arr =>{
     let hashTable = {}, max = 0, result = []
     for(let i=0; i<arr.length; i++){
         if(!(arr[i] in hashTable)){
             hashTable[arr[i]] = 1
         }else{
             hashTable[arr[i]] += 1
         }
         if (arr[i] > max) {
             max = arr[i]
         }
     }
     for(let j=0; j<= max; j++){
         if(j in hashTable){
             for(let i=0; i<hashTable[j];i++){
                 result.push(j)
             }
         }
     }
     return result
 }