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1到100之间的偶数之和

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//方法一
 var sum =0;
 for (int i = 2; i <= 100; i+=2) {
     sum+=i;
 }
 System.out.println(sum);

//方法二
 var s=0;
 var a=1;
 var b=100;
 for (; a <= b; a++) {
     s+=a%2==0?a:0;
 }
 System.out.println(s);

逢七过

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//方法一
 for (int i = 0; i < 100; i++) {
     if (i % 10 == 7 || i / 10 % 10 == 7 || i % 7 == 0) {
         System.out.println("过");
         continue;
     }
     System.out.println(i);
 }

//方法二
 for (int i = 0; i < 100; i++) {
     String d = (i % 10 == 7 || i / 10 % 10 == 7 || i % 7 == 0 ? "过" : String.valueOf(i));
 System.out.println(d);
 }

求和

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List<Integer> list = List.of(1, 2, 3, 4, 5, 6);
  var sm =0;
  for (int i = 0; i < list.size(); i++) {
      sm+=list.get(i);
  }
  System.out.println(sm);

二分半查找

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@Test
   public void test(){
    int[] arr = {1, 2, 3, 4, 5, 6, 7};
    System.out.println(bina(arr, 4));
}
private static int bina(int[]arr,int number) {
    var min=0;
    var max=arr.length-1;

    while (true) {
        if (min > max) {
            return -1;
        }
        int mid =(min+max)/2;
        if (arr[mid] > number) {
            max=mid-1;
        } else if (arr[mid] < number) {
            min = mid + 1;
        } else {
            return mid;
        }
    }
}

冒泡排序

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@Test
 public void test1(){
     int[] arr = {2, 5, 3, 4, 1};
     for (int i = 0; i < arr.length-1; i++) {
         for (int j = 0; j < arr.length-1-i; j++) {
             if (arr[j] > arr[j+1]) {
                 int temp =arr[j];
                 arr[j] = arr[j + 1];
                 arr[j+1]=temp;
             }
         }
     }
     for (int i = 0; i < arr.length; i++) {
         System.out.print(arr[i]+" ");
     }
 }

选择排序

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@Test
public void test2(){
    int[] arr = {2, 3, 1, 5, 4};

    for (int i = 0; i < arr.length-1; i++) {
        for (int j = i+1; j < arr.length; j++) {
            if (arr[i] > arr[j]) {
                int temp =arr[i];
                arr[i] = arr[j];
                arr[j]=temp;
            }
        }
    }
    for (int i = 0; i < arr.length; i++) {
        System.out.println(arr[i]);
    }

}