冒泡排序

function bubbleSort(arr) {
  for(let i = 0; i < arr.length; i++) {
    for(let j = 1; j < arr.length - 1 - i; j ++) {
      if(arr[j - 1] > arr[j]) {
        const temp = arr[j];
        arr[j] = arr[j - 1];
        arr[j - 1] = temp;
      }
    }
  }
}

bubbleSort([5,4,3,2,1])

选择排序

function selectSort(arr) {
  let minIndex = 0
  for(let i = 0; i < arr.length; i++) {
    minIndex = i;
    for(let j = i; j < arr.length - 1; j ++) {
      if(arr[j] > arr[j+1]) {
        minIndex = j+1;
      }
    }
    if(minIndex !== i) {
      [arr[i], arr[minIndex]] = [arr[minIndex], arr[i]]
    }
  }
}

selectSort([5,4,3,2,1])

插入排序

function insertSort(arr) {
  const len = arr.length;
  for(let i = 1; i < len; i ++) {
    if(arr[i - 1] > arr[i]) {
      const temp = arr[i];
      let j = i;
      while(j > 0 && temp < arr[j - 1]) {
        arr[j] = arr[j-1];
        j--;
      }
      arr[j] = temp;
    }
  }
  console.log(arr)
}

insertSort([5,4,3,2,1])

归并排序

递归

function mergeSort(arr) {
  const len = arr.length;
  if(len <= 1) {
    return arr;
  }

  const mid = Math.floor(len / 2);

  const leftArr = mergeSort(arr.slice(0, mid))

  const rightArr = mergeSort(arr.slice(mid, len));

  const res = mergeArr(leftArr, rightArr);

  console.log(res)
  return res;
}

function mergeArr(left, right) {
  const leftLen = left.length;
  const rightLen = right.length;

  let l = 0;
  let r = 0;
  let res = [];
  while(l < leftLen && r < rightLen) {
    if(left[l] < right[r]) {
      res.push(left[l]);
      l++;
    } else {
      res.push(right[r]);
      r++;
    }
  }
  if(l < leftLen) {
    res = res.concat(left.slice(l))
  } else {
    res = res.concat(right.slice(r))
  }
  return res
}


mergeSort([5,4,3,2,1])