常见的算法练习

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(1):字符串 反转 比如:I Like you 变成 you Like I

public class SwapString {/** * 思路:先把字符串的第一个字符与最后一个字符进行调换位置 *  * @param arr * @param begin * @param end */public static void swap(char[]arr,int begin,int end){while(begin < end){char temp = arr[begin];arr[begin] = arr[end];arr[end] = temp;begin ++;end --;}}public static String swapString(String str){char []arr = str.toCharArray();swap(arr,0,str.length()-1);int begin = 0;for(int i=1;i<arr.length;i++){if(arr[i] ==' '){swap(arr,begin,i-1);begin = i + 1;}}swap(arr,begin,arr.length - 1);return new String(arr);}public static void main(String[] args) {Scanner in = new Scanner(System.in);String str = in.nextLine();System.out.println(swapString(str));}}
2:要求:输入二个字符串,从第一个字符串中删除第二个字符串中所有的字符,输出删除后第一个字符串。
 * 比如输入:They are students.”和”aeiou”,输出”Thy r stdnts.”

public class DelCommonStr {public static String delString(String str1,String str2){String newString = "";for(int i=0;i<str1.length();i++){boolean flag = false;for(int j=0;j<str2.length();j++){if(str1.charAt(i) == str2.c
public class ListAllNum {public static void printList(int m,int n,List<Integer>list){if(m == 0){System.out.println(list); return;}if(n<=0 || m<0){return;}List list1 = new ArrayList<>(list);printList(m, n-1, list);list1.add(n);printList(m-n, n-1, list1);}public static void main(String[] args) {Scanner in = new Scanner(System.in);int n = in.nextInt();int m  = in.nextInt();List<Integer> list = new ArrayList<>();int up = n > m ? m : n;printList(m,up,list);
}

(3:要求:输入两个整数 n 和 m,从数列1,2,3.......n 中随意取几个数,使其和等于 m,要求将其中所有的可能组合列出来

public class ListAllNum {public static void printList(int m,int n,List<Integer>list){if(m == 0){System.out.println(list); return;}if(n<=0 || m<0){return;}List list1 = new ArrayList<>(list);printList(m, n-1, list);list1.add(n);printList(m-n, n-1, list1);}public static void main(String[] args) {Scanner in = new Scanner(System.in);int n = in.nextInt();int m  = in.nextInt();List<Integer> list = new ArrayList<>();int up = n > m ? m : n;printList(m,up,list);}}

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