[Bubble Sort + Custom Conditions] Point to Offer 45. Arrange the array into the smallest number

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Daily quiz 2021.04.04

• leetcode original title link: leetcode-cn.com/problems/so…
• Difficulty: Moderate
• Method: bubble sort

topic

• Input an array of non-negative integers, concatenate all the numbers in the array into a number, and print the smallest one of all the numbers that can be concatenated.

Example

• Example 1

输入: [10,2]
输出: "102"
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• Example 2

输入: [3,30,34,5,9]
输出: "3033459"
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Problem solving ideas

• According to the meaning of the question: the sorting algorithm needs to be used, but the sorting conditions need to be customized
• Key Point: Custom Sort Order
  • analyze:[3,30,34,5,9]
  • Take0和1 the element with the subscript and compare it in combination => 330 与 303, if the subscript is a small number spliced ​​before, you need to exchange the value 1of the element with the subscript .0和1
  • Because the bubble sort will n - 1traverse several times, each time the largest is placed at the end of the array.
• After the n - 1round traversal, the elements in the array will be neatly arranged in a custom order.

expand

• The so-called stability: is the relative position of two equal elements in the array, whether it changes after sorting
  • No change: stable sorting
  • Changed: unstable sorting

Bubble sort (whoever is older stands on the right)

• The numbers in the array are compared in pairs, each time the largest number is moved to the end of the array.
• A variable is also required to record whether a swap has occurred this round .
  • If there is no exchange in this round, then the data in the array has all been arranged in order, and jump out of the loop directlybreak
  • On the contrary, it has not been completely
• Time complexity: o(n^2)
• Space complexity: o(1)

swapexchange skills

• Requirement: Swap two numbers without using a third intermediate variable
• The way of adding and then subtracting
• Bit operation:

arr[i] = arr[i] ^ arr[j];
arr[j] = arr[j] ^ arr[i];
arr[i] = arr[i] ^ arr[j];
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Quick sort (classic topic)

• 215. Kth largest element in an array

ACcode

var minNumber = function(nums) {
  // 排序好了之后再拼接在一起
  function bubbleSort(arr) {
    let alen = arr.length, isChange = false;
    for(let i = 0; i < alen; i++) {
      if(isChange) break;
      isChange = true;
      for(let j = 0; j < alen - 1; j++) {
        // console.log(arr[j + 1] + ''+  arr[j],arr[j] + '' + arr[j + 1])
        if((arr[j + 1] + '' +  arr[j]) <= (arr[j] + '' + arr[j + 1])){
          arr[j + 1] = arr[j + 1] + arr[j];
          arr[j] = arr[j + 1] - arr[j];
          arr[j + 1] = arr[j + 1] - arr[j];
          isChange = false;
        }
      }
    }
  }
  bubbleSort(nums);
  // console.log(nums)
  let len = nums.length, ans = '';
  for(let i = 0; i < len; i++) {
    ans += nums[i];
  }
  return ans;
};
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Summarize

• It does not matter what sorting algorithm is used, the important test point is: the conversion of the conditions of the sorting algorithm.