今天在微信公众号看到一篇“每个程序员半小时内必须解决的5个编程问题”,发现自己也不完全会,在网上搜罗做了整理,以便不时之需。
问题1
使用for循环、while循环和递归写出3个函数来计算给定数列的总和。
问题2
编写一个交错合并列表元素的函数。例如:给定的两个列表为[a,B,C]和[1,2,3],函数返回[a,1,B,2,C,3]。
问题3
编写一个计算前100位斐波那契数的函数。根据定义,斐波那契序列的前两位数字是0和1,随后的每个数字是前两个数字的和。例如,前10位斐波那契数为:0,1,1,2,3,5,8,13,21,34。
问题4
编写一个能将给定非负整数列表中的数字排列成最大数字的函数。例如,给定[50,2,1,9],最大数字为95021。
问题5
编写一个在1,2,…,9(顺序不能变)数字之间插入+或-或什么都不插入,使得计算结果总是100的程序,并输出所有的可能性。例如:1 + 2 + 34 – 5 + 67 – 8 + 9 = 100。
问题1:
public class SumTest { public static void whileMethod(int[] array) { if (null == array || array.length == 0) { return; } int sum = 0; int i = 0; while (i < array.length) { sum += array[i]; i++; } System.out.println("Sum result is while : " + sum); } public static void forMethod(int[] array) { if (null == array || array.length == 0) { return; } int sum = 0; int i = 0; for (int num: array) { sum += num; } System.out.println("Sum result is for : " + sum); } public static int recursiveMethod(int[] array, int i) { if (null == array || array.length == 0) { return 0; } if (i < array.length) { return array[i] + recursiveMethod(array, i + 1); } return 0; } public static void main(String[] args){ int[] array = {1, 2, 3, 4, 5, 6, 7}; whileMethod(array); forMethod(array); System.out.println(recursiveMethod(array, 0)); } }
问题2:
public class ListMerge { public static String[] mergeList(String[] arg1, String[] arg2) { String[] arr = new String[arg1.length + arg2.length]; int i, j; for (i = 0, j = 0; i < arg1.length; i++) { j = 2 * i; if (j > 2 * arg2.length){ j = arg2.length + i; } arr[j] = arg1[i]; } for (i = 0, j = 0; i < arg2.length; i++) { j = 2 * i + 1; if (j > 2 * arg1.length) { j = arg1.length + 1; } arr[j] = arg2[i]; } return arr; } public static void main(String[] args){ String[] arr1 = { "a", "B", "c", "D", "e" }; String[] arr2 = { "1", "2", "3" }; String[] arr = mergeList(arr1, arr2); System.out.println(Arrays.toString(arr)); } }
问题3:
public class Fibonacci { private static int getNum(int num) { int count = 0; if (num <= 1) { count = 0; } else if (num == 2) { count = 1; } else { count = getNum(num - 1) + getNum(num - 2); } return count; } private static String getSum(int num) { String numStr = ""; for (int i = 0; i <= num; i++) { numStr = getNum(i) + ","; } numStr = numStr.substring(0, numStr.length() - 1); return numStr; } public static void main(String[] args){ System.out.println("The number is : " + getSum(100)); } }
问题4:
public class MaxValue { private static Integer[] VALUES = { 50, 2, 100, 99, 5, 7, 51,50 ,11}; public static void main(String[] args){ Arrays.sort(VALUES, new Comparator<Integer>() { public int compare(Integer o1, Integer o2) { String v1 = o1.toString(); String v2 = o2.toString(); return (v1 + v2).compareTo(v2 + v1) * - 1; } }); String result = ""; for (Integer integer: VALUES) { result += integer.toString(); } System.out.println(result); } }
问题5:
public class SameSum { private static int TARGET_SUM = 100; private static int[] VALUES = { 1, 2, 3, 4, 5, 6, 7, 8, 9 }; private static ArrayList add(int digit, String sign, ArrayList branches) { for (int i = 0; i < branches.size(); i++) { branches.set(i, digit + sign + branches.get(i)); } return branches; } private static ArrayList f(int sum, int number, int index) { int digit = Math.abs(number % 10); if (index >= VALUES.length) { if (sum == number) { ArrayList result = new ArrayList(); result.add(Integer.toString(digit)); return result; } else { return new ArrayList(); } } ArrayList branch1 = f(sum - number, VALUES[index], index + 1); ArrayList branch2 = f(sum - number, -VALUES[index], index + 1); int concatenatedNumber = number >= 0 ? 10 * number + VALUES[index] : 10 * number - VALUES[index]; ArrayList branch3 = f(sum, concatenatedNumber, index + 1); ArrayList results = new ArrayList(); results.addAll(add(digit, "+", branch1)); results.addAll(add(digit, "-", branch2)); results.addAll(add(digit, "", branch3)); return results; } public static void main(String[] args) { ArrayList list = f(TARGET_SUM, VALUES[0], 1); for(int i=0;i<list.size();i++) { System.out.println(list.get(i)); } } }