PS:后续添加 没有顺序了 搜到什么看什么吧

查找子串

public static void main(String[] args) {
        String s = "1234567890";
        int pos1 = s.indexOf("23");
        int pos2 = s.indexOf("A");
        System.out.println(pos1);  // 1
        System.out.println(pos2);  // -1
    }

数据初始化

int []a = new int[10];
        Arrays.fill(a,10);
        Arrays.stream(a).forEach(System.out::println);

最大公约数

//公倍数 两数相乘  除以公约数
#include<bits/stdc++.h>
using namespace std;
int a[40] = {1,2};
int main()
{
    cout << __gcd(12,6);
    //cout << __INT32_MAX__ << endl;
}

1.accumulate求和

public static void main(String[] args) {
        int []a = new int[10];
        Arrays.fill(a,10);
        Arrays.stream(a).sum();
        Arrays.stream(a).forEach(System.out::println);
}

4. bitset

可实现十进制和二进制的互换

Integer a= 16;
 Integer.toHexString(a);
```c


### 5.copy 
```c
  int []a = new int[]{12,3,4,5,6};
  int[] ints = Arrays.copyOfRange(a, 1, 3);
  Arrays.stream(ints).forEach(System.out::println);

6. count

int []a = new int[]{12,3,4,3,6};
  long count = Arrays.stream(a).filter(o -> o == 3).count();
  System.out.println(count);

9 find

public static void main(String[] args) {
        int []a = new int[]{1,2,3,4,5};
        int i = Arrays.binarySearch(a, 4);
        System.out.println(i);
    }

14.replace_if() 满足条件的替换

String s = "12345";
  String c = s.replace('4', 'C');
  System.out.println(c);

15.strstr() char*类型找到子串

String s = "12345";
  int i = s.indexOf("34");
  System.out.println(i);

16. substr() 截取字符

String s = "12345";
 String substring = s.substring(0, 4);

19. 去重复unique() 必须已经排序

Integer []a = new Integer[]{1,2,3,4,5,5};
   List<Integer> collect = Arrays.stream(a).distinct().collect(Collectors.toList());
   collect.forEach(System.out::println);

交并集

Integer []a = new Integer[]{1,2,3};
   Integer []b = new Integer[]{3,4,5};
    HashSet hashSetA = new HashSet<>(List.of(a));
    HashSet hashSetB = new HashSet<>(List.of(b));
//        hashSetA.retainAll(hashSetB);  交集
//        hashSetA.addAll(hashSetB);   并集
//        hashSetA.removeAll(hashSetB);  差集
    hashSetA.forEach(System.out::println);

得到最大值最小值

ArrayList<Integer> ints = new ArrayList<>(Arrays.asList(1,2,3,4,5,6)) ;
        Optional<Integer> max = ints.stream().max((a, b) -> {
            return a.compareTo(b);
        });
        System.out.println(max.get());