阶乘 16进制转换 输出1-9所有的排列组合
阶乘的代码public class Factorial {public static Integer factorial(int i){if(i<0){System.out.println("输入错误");return null;}else if(i==0){return 1;}else{if(i-1 > 1){return i*factorial(i-1);}else{return i;}}}public static void main(String[] args) {for(int num=-100;num<10;num++){System.out.println(num+ "的阶乘是"+ factorial(num));}}}
负数不知道怎么处理好
16进制转换为10进制整数public class Hex2Decimal {
//用Integer的方法/*public static int hex2Decimal(String str){return Integer.parseInt(str, 16);}*///用Character的方法public static int hex2Decimal(String str){int len = str.length();int sum = 0;for(int i=0;i<len;i++){char c = str.charAt(i);int n = Character.digit(c, 16);sum += n*(1<<(4*i));}return sum;}public static void main(String[] args) {String st = "aa";System.out.println(hex2Decimal(st));}} 输出1-9所有的排列组合public class Permutations {
private int[] a = new int; public void init(){ for(int i=1;i<=9;i++){ a=i; } } private void printNumber(){ for(int j=1;j<=9;j++){ System.out.print(a+" "); } System.out.println(); } public void range(int index){ if(index==9){ printNumber(); } else{ for(int i=index;i<=9;i++){ int k = index; swap(i,k); range(k+1); swap(i,k); } } } private void swap(int i, int j){ int temp =a; a=a; a=temp; } public static void main(String[] args) { Permutations p = new Permutations(); p.init(); p.range(1); }}
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