java面试常见到的算法.doc

Java面试中遇到的一些经典算法题目1.写一个方法，用一个for循环打印九九乘法表 /* */* * 打印九九乘法口诀表 */ public void nineNineMulitTable() for (int i = 1,j = 1; j = 9; i+) System.out.print(i+*+j+=+i*j+ ); if(i=j) i=0; j+; System.out.println(); 2.给定一个java.util.Date对象，如何转化为”2007-3-22 20:23:22”格式的字符串 /* */* * 将某个日期以固定格式转化成字符串 * param date * return str */ public String date2FormatStr(Date date) SimpleDateFormat sdf = new SimpleDateFormat(yyyy-MM-dd HH:mm:ss); String str = sdf.format(date); return str; 3.写一个方法，能够判断任意一个整数是否素数 /* */* * 判断任意一个整数是否素数 * param num * return boolean */ public boolean isPrimeNumber(int num) for (int i = 2; i = Math.sqrt(num); i+) if(num%i=0) return false; return true; 4.写一个方法，输入任意一个整数，返回它的阶乘 /* */* *获得任意一个整数的阶乘 *param n *returnn! */ public int factorial(int num) /递归 if(num = 1) return 1; return num*factorial(num-1); 5.写一个方法，用二分查找法判断任意整数在任意整数数组里面是否存在，若存在就返回它在数组中的索引位置，不存在返回-1 /* */* *二分查找特定整数在整型数组中的位置(递归) *param dataset *param data *param beginIndex *param endIndex *return index */ public int binarySearch(int dataset,int data,int beginIndex,int endIndex) int midIndex = (beginIndex+endIndex)/2; /如果查找的数要比开始索引的数据要小或者是比结束索引的书要大，或者开始查找的索引值大于结束的索引值返回-1没有查到 if(data datasetendIndex|beginIndexendIndex) return -1; if(data datasetmidIndex) return binarySearch(dataset,data,midIndex+1,endIndex); else return midIndex; /* */* *二分查找特定整数在整型数组中的位置(非递归) *param dataset *param data *return index */ public int binarySearch(int dataset ,int data) int beginIndex = 0; int endIndex = dataset.length - 1; int midIndex = -1; if(data datasetendIndex|beginIndexendIndex) return -1; while(beginIndex = endIndex) midIndex = (beginIndex+endIndex)/2; if(data datasetmidIndex) beginIndex = midIndex+1; else return midIndex; return -1; 一，冒泡排序：package com.sort;import java.util.Random;public class No1Maopao public static void main(String args) Random rd = new Random();/生成随即数组 int src = new int10; for(int i=0;i10;i+) srci=rd.nextInt(100); /排序前打印数组所有元素 for(int i:src) System.out.println(i); System.out.println(-可爱的分割线-); src = sort(src);/排序后打印数组所有元素 for(int i:src) System.out.println(i); public static int sort(int src) for (int i = 0; i src.length; i+) for(int j=i;jsrc.length;j+) if(srcjsrci) int temp = srcj; srcj=srci; srci=temp; return src; 二、选择排序：package com.sort;import java.util.Random;public class No2XuanZhe public static void main(String args) Random rd = new Random(); int src = new int10; for (int i = 0; i 10; i+) srci = rd.nextInt(100); for (int i : src) System.out.println(i); System.out.println(-可爱的分割线-); src = sort(src); for (int i : src) System.out.println(i); public static int sort(int src) int min; for (int i = 0; i src.length; i+) min = srci; for (int j = i + 1; j src.length; j+) if (srcj min) min = srcj; int temp = srci; srci = srcj; srcj = temp; return src; 三、插入排序：package com.sort;import java.util.Random;public class No3ChaRu public static void main(String args) Random rd = new Random(); int src = new int10; for (int i = 0; i 10; i+) srci = rd.nextInt(100); for (int i : src) System.out.println(i); System.out.println(-可爱的分割线-); src = sort(src); for (int i : src) System.out.println(i); public static int sort(int src) int in, out; for (in = 1; in 0 & srcout - 1 = temp) srcout = srcout - 1; -out; srcout = temp; return src; 四、希尔排序：package com.sort;import java.util.Random;public class No4Xier public static void main(String args) Random rd = new Random(); int src = new int10; for (int i = 0; i 10; i+) srci = rd.nextInt(100); for (int i : src) System.out.println(i); System.out.println(-可爱的分割线-); src = sort(src); for (int i : src) System.out.println(i); public static int sort(int src) int len = src.length; int temp, i, j; int h = 1; while (h 0) for (i = h; i h - 1 & srcj - h = temp) srcj = srcj - h; j -= h; srcj = temp; h = (h - 1) / 3; return src; 五、快速排序：public class No5Kuaisu public static void quickSort(int array) quickSort(array, 0, array.length - 1); private static void quickSort(int array, int low, int high) if (low high) int p = partition(array, low, high); quickSort(array, low, p - 1); quickSort(array, p + 1, high); private static int partition(int array, int low, int high) int s = arrayhigh; int i = low - 1; for (int j = low; j high; j+) if (arrayj s) i+; swap(array, i, j); swap(array, +i, high); return i; private static void swap(int array, int i, int j) int temp; temp = arrayi; arrayi = arrayj; arrayj = temp; public static void main(String args) Random rd = new Random(); int src = new int10; for (int i = 0; i 10; i+) srci = rd.nextInt(100); for (int i : src) System.out.println(i); System.out.println(-可爱的分割线-); quickSort(src); for (int i : src) System.out.println(i); System.out.println(-可爱的分割线-); 输入几个符号 (每个符号是由任意可见字符组成的字符串), 输出这些符号的全部组合.如:VLTest s abc, bc, efg 回车输出:abc,bc,efg, abcbc, abcefg, bcefg, abcbcefg.注意: 输入符号个数不固定, 输出的组合中不计顺序，即abcefg 与efgabc 属于同一个结果/Java实现：public class Test public static void main(String args) int num = args.length;for (int i = 1; i = num; i+) Combine(args, i);private static void Combine(String input, int num) String b = ;Combine(input, num, b, 0, input.length);private static void Combine(String a, int num, String b, int low, int high) if (num = 0) System.out