面經-演算法

1. 查詢文字中出現最多的字元，和位置

   map記錄字元和數量

   #pyhon版本
   def wordcount(str):
       h =[]
       dict = {}
       max = 0
       maxkey = ""
       chars = str.split()
       for c in chars:
           if c not in dict:
               dict[c] = 1
               continue
           dict[c] = dict[c] + 1
           if max < dict[c]:
               max = dict[c]
               maxkey = c
       for index, c in enumerate(chars):
           if c == maxkey:
               h.append(index)
       print(h)
       print(dict)
       print(maxkey)
   

   private static void findMostStr(String s) {
       HashMap<String, Integer> map = new HashMap<>();
       ArrayList<Integer> localList = new ArrayList<>();
       String[] ss = s.split(" ");
       int max = 0;
       String maxKey = null;
       for (String str : ss) {
           if (!map.containsKey(str)){
               map.put(str, 0);
               continue;
           }
           map.put(str, map.get(str)+1);
           if (max < map.get(str)) {
               max = map.get(str);
               maxKey = str;
           }
       }
       for(int i = 0; i < ss.length; i++) {
           if (ss[i].equals(maxKey)) {
               localList.add(i);
           }
       }
       System.out.println(localList);
   }
   

2. 快速排序

   【全網最清晰快速排序，看完快排思想和程式碼全部通透，不通透你打我！】https://www.bilibili.com/video/BV1vP411g7J3?vd_source=b5b6b7b62043766d7076c5c42dfe4aef

   找到基準，把比基準小的數放入基準前方，比基準大的數放入基準後面，然後分而治之

   private static void quickSort(int[] a, int low, int high) {
    if (low < high) {
           //        找到當前基準位置
           int p = partition(a,low,high);
           quickSort(a,low, p - 1);
           quickSort(a, p + 1, high);
       }
           
    }
   

   private static int partition(int[] a, int low, int high) {
       int j = a[low];
       while(low < high) {
           while (low < high && a[high] >= j) {
               high --;
           }
           a[low] = a[high];
           while (low < high && a[low] <= j) {
               low ++;
           }
           a[high] = a[low];
       }
       a[low] = j;
       return low;
   }
   

   #pyhon版
   def partiton(a, low, high):
       point = a[low]
       while (low < high) :
           while (low < high and a[high] >= point):
               high = high - 1
           a[low] = a[high]
           while(low < high and a[low] <= point):
               low = low + 1
           a[high] = a[low]
       a[low] = point
       return low
   
   
   def quicksort(a, low, high):
       if (low < high):
           p = partiton(a,low, high)
           quicksort(a, low, p - 1)
           quicksort(a, p + 1, high)
   

3. 最大不重複字串字串