LeetCode之常用函数

 收集了 LeetCode 面试经典150 & LeetCode 热题100中常用的函数与技巧

 LeetCode之数组/字符串

地址链接

    public static void main(String[] args) {// 1. 数组排序int[] array = new int[]{3, 7, 5, 2};Arrays.sort(array);// 结果: [2, 3, 5, 7]System.out.println(Arrays.toString(array));// 2. 数组拷贝int[] arrayOld = new int[]{1, 2, 3, 4, 5};int[] arrayNew = new int[5];System.arraycopy(arrayOld, 0, arrayNew, 0, arrayOld.length - 1);// 结果: [1, 2, 3, 4, 5]System.out.println(Arrays.toString(arrayOld));// 结果: [1, 2, 3, 4, 0]System.out.println(Arrays.toString(arrayNew));// 3. 最大值最小值int max = Math.max(2, 3);int min = Math.min(2, 3);// 结果 3-2System.out.println(max + "-" + min);// 4. 随机数生成Random random = new Random();int randomInt = random.nextInt(10);// 结果: 8System.out.println(randomInt);// 5. HashMapMap<String, String> hashMap = Maps.newHashMap();hashMap.put("1", "1");hashMap.put("2", "2");hashMap.put("3", "3");// 结果: trueSystem.out.println(hashMap.containsKey("1"));// 6. ArrayListList<String> arrayList = Lists.newArrayList("1", "2", "3");arrayList.set(2, "4");arrayList.remove(1);// 结果: [1, 4]System.out.println(arrayList);// 7. 数组创建int[] arr1 = new int[3];arr1[0] = 1;int[] arr2 = {1, 2, 3};int[] arr3 = new int[]{1,2,3};// 结果: [1, 0, 0]System.out.println(Arrays.toString(arr1));// 结果: [1, 2, 3]System.out.println(Arrays.toString(arr2));// 结果: [1, 2, 3]System.out.println(Arrays.toString(arr3));// 8. 字符串String str = "hello world";char[] charArray = str.toCharArray();// 结果: lSystem.out.println(str.charAt(3));// 结果: [h, e, l, l, o,  , w, o, r, l, d]System.out.println(Arrays.toString(charArray));// 9. switch语句String condition = "a";// 结果: aswitch (condition) {case "a":System.out.println("a");break;case "b":System.out.println("b");break;default:System.out.println("c");}// 10. 可变字符串StringBuilder sb = new StringBuilder();sb.append("1");sb.append("2");sb.append("3");// 结果: 123System.out.println(sb.toString());// 11. 字符串去空格String strTrim = " tes t ";String trim = strTrim.trim();// 结果: tes tSystem.out.println(trim);// 结果: 5System.out.println(strTrim.lastIndexOf("t"));// 12. 字符串截取String strSub = "test subString";String substring = strSub.substring(5, 8);System.out.println(substring);// 13. 正则&字符串拼接String string = " hello world ";String trim1 = string.trim();// 结果: hello worldSystem.out.println(trim1);String[] split = trim1.split("\\s+");List<String> strings = Arrays.asList(split);// 结果: [hello, world]System.out.println(strings);Collections.reverse(strings);// 结果: [world, hello]System.out.println(strings);// 结果: world,helloString join = String.join(",", strings);System.out.println(join);}

LeetCode之双指针

地址链接

    public static void main(String[] args) {// 1. Char操作char a = '1';char b = 'b';// 判断是否字符或数组// 结果: trueSystem.out.println(Character.isLetter(b));// 结果: trueSystem.out.println(Character.isDigit(a));// 结果: trueSystem.out.println(Character.isLetterOrDigit(a));char c = 'C';// 结果: trueSystem.out.println(Character.toLowerCase(c));// 2. 可变字符串反转StringBuilder sb = new StringBuilder();sb.append("1");sb.append("2");sb.append("3");// 结果: 321System.out.println(sb.reverse());}

LeetCode之滑动窗口

地址链接

    public static void main(String[] args) {// 1. Integer最大最小值int min = Integer.MIN_VALUE;int max = Integer.MAX_VALUE;// 结果: -2147483648System.out.println(min);// 结果: 2147483648System.out.println(max);// 2. Set操作Set<String> set = Sets.newHashSet("1", "2", "2", "3");// 结果: [1, 2, 3]System.out.println(set);// 结果: trueSystem.out.println(set.contains("2"));// 结果: trueSystem.out.println(set.remove("3"));// 结果: [1, 2]System.out.println(set);}