js實現多種排序算法（算法導論第二章）

1. 插入排序：

   var a = [1,7,4,2,17,13,9]

   function insertionSort(arr){

   arr.map((d,index)=>{
          let i = index
          while(d<arr[i-1]&&i-1>0){
              [arr[i-1],arr[i]]=[arr[i],arr[i-1]]
              i--
          }
      })

   }
   insertionSort(a)

2. 歸併排序（非hack）

   function merge (arr,l,m,r){

   var left = []
      var right = []
      for (let i =l;i<m;i++){
          // console.log(i)
          left.push(arr[i])
      }
      for(let j = m;j<=r;j++){
          right.push(arr[j])
          // console.log(j)
      }
      left.push(Infinity)
      right.push(Infinity)
      console.log(left,right)
      var i =0
      var j =0
      for(let k =l;k<r+1;k++){
   
          if(left[i]<right[j]){
              arr[k]=left[i]
              i++
          }else{
              arr[k]=right[j]
              j++
          }
      }

   }
   function mergeSort(arr,l,r){

   if(r>l){
          var m=Math.ceil((l+r)/2)
          // console.log(m)
          mergeSort(arr,l,m-1)
          mergeSort(arr,m,r)
          merge(arr,l,m,r)
      }

   }

3. 歸併排序（酷炫簡單）

   function merge(left, right) {

   var tmp = [];
   
    while (left.length && right.length) {
      if (left[0] < right[0])
        tmp.push(left.shift());
      else
        tmp.push(right.shift());
    }
   
    return tmp.concat(left, right);

   }

   function mergeSort(a) {

   if (a.length === 1) 
      return a;
   
    var mid = ~~(a.length / 2)
      , left = a.slice(0, mid)
      , right = a.slice(mid);
   
    return merge(mergeSort(left), mergeSort(right));

   }