给定一个数组a，长度为n，求数组中所有两个元素相加之和为N的小标i和j
import java.util.*; public class Main { public static void main(String[] args) { Scanner sc = new Scanner(System.in); int n = sc.nextInt(); int N = sc.nextInt(); int[] arr = new int[n]; Map<Integer, Integer> map = new HashMap<>(); for (int i=0;i<n;i++){ arr[i] = sc.nextInt(); map.put(arr[i],i); } for (int i=0;i<n;i++){ int complement = N - arr[i]; if (map.containsKey(complement)){ System.out.println(i+":"+map.get(complement)); } } } }
三个线程的名字分别为0,1,2，每个线程输出十次，按照012012012. . .的方式输出
public class Main { //用来记录前一个数的值 int x=-1; public static void main(String[] args){ Main m = new Main(); new Thread(m.new RunnableA("0")).start(); new Thread(m.new RunnableB("1")).start(); new Thread(m.new RunnableC("2")).start(); } class RunnableA implements Runnable{ private String name; public RunnableA(String name) { this.name = name; } @Override public void run(){ for(int i=0;i<10;i++){ synchronized (Main.class){ if(x == 1 || x == 0){ try { Main.class.wait(); } catch (InterruptedException e) { e.printStackTrace(); } i--; continue; } else { System.out.print(name); x = 0; Main.class.notifyAll(); } } } } } class RunnableB implements Runnable{ private String name; public RunnableB(String name){ this.name = name; } @Override public void run(){ for(int i=0;i<10;i++){ synchronized (Main.class){ if(x == 1 || x == 2){ try { Main.class.wait(); } catch (InterruptedException e) { e.printStackTrace(); } i--; continue; } else { System.out.print(name); x = 1; Main.class.notifyAll(); } } } } } class RunnableC implements Runnable{ private String name; public RunnableC(String name){ this.name = name; } @Override public void run(){ for(int i=0;i<10;i++){ synchronized (Main.class){ if(x == 0 || x == 2){ try { Main.class.wait(); } catch (InterruptedException e) { e.printStackTrace(); } i--; continue; } else { System.out.print(name); x = 2; Main.class.notifyAll(); } } } } } }
给定一个字符串，得到这个数组按顺序最小的字符串输出，最小的输出个数为s
- 例如：str=1584632 s=3 输出：132
public class Main { public static void main(String[] args) { Scanner sc1 = new Scanner(System.in); Scanner sc2 = new Scanner(System.in); //输入一个字符串 String str = sc1.nextLine(); //得到剩余的最小的个数 int s = sc2.nextInt(); //将字符串变成 int[] int[] arr = new int[str.length()]; for (int i=0;i<arr.length;i++){ arr[i] = Integer.parseInt(str.substring(i,i+1)); } //将值以及对应的下标存入HashMap中，并将值存入list列表中 HashMap<Integer,Integer> map = new HashMap<>(); List<Integer> list = new ArrayList<>(); for (int i=0;i<arr.length;i++){ map.put(arr[i],i); list.add(arr[i]); } //给列表进行排序 Collections.sort(list); //将最小的 s 个整型存入HashMap中 Map<Integer,Integer> map1 = new HashMap<>(); for (int i=0;i<s;i++){ map1.put(list.get(i),map.get(list.get(i))); } //对这个HashMap进行排序，按照 value 从小到大进行排序 List<Map.Entry<Integer,Integer>> list1 = new ArrayList<>(); Set<Map.Entry<Integer, Integer>> entries = map1.entrySet(); for (Map.Entry<Integer,Integer> e : entries){ list1.add(e); } Collections.sort(list1, new Comparator<Map.Entry<Integer, Integer>>() { @Override public int compare(Map.Entry<Integer, Integer> o1, Map.Entry<Integer, Integer> o2) { return o1.getValue() - o2.getValue(); } }); //排序完成后进行输出，如果首位为 0 那么跳过 for (Map.Entry<Integer,Integer> m : list1){ if (m.getKey() != 0){ System.out.print(m.getKey()); } } } }
比较版本号：第二个版本号大于第一个那么就返回true，否则返回false
import java.util.*; public class Main { public static void main(String[] args) { Scanner sc = new Scanner(System.in); int n = sc.nextInt(); for (int q = 0;q<n;q++){ //记得转义，并且next()方法遇到空格就会结束，而nextLine()不会 //比如: 你好 你好 /** * 记得转义，并且next()方法遇到空格就会结束，而nextLine()不会 * 比如: 你好 你好 * nextLine()读取到: 你好 你好 * next()读取到: 你好 */ String[] str1 = sc.next().split("\\."); String[] str2 = sc.next().split("\\."); int maxIndex = Math.max(str1.length,str2.length); int[] arr1 = new int[maxIndex]; int[] arr2 = new int[maxIndex]; for (int i=0;i<str1.length;i++){ //字符串变整数 arr1[i] = Integer.valueOf(str1[i]); } for (int i=0;i<str2.length;i++){ arr2[i] = Integer.valueOf(str2[i]); } for (int i=0;i<=maxIndex;i++){ //两个字符串一样长并且都相等 if (i==maxIndex){ System.out.println("false"); break; } else { if (arr1[i]<arr2[i]){ System.out.println("true"); break; } else if (arr1[i]>arr2[i]){ System.out.println("false"); break; } } } } } }
一个数的各个位的平方和得到一个数，如果得到的结果为1，则返回true，否则继续这行这个操作
- 例如：19
- 1^2+9^2=82
- 8^2+2^2=68
- 6^2+8^2=100
- 1^2+0^2+0^2=1
- 则返回true
import java.util.*; public class Main { public static void main(String[] args) { Scanner sc = new Scanner(System.in); int n = sc.nextInt(); for (int i = 0; i < n; i++) { int t = sc.nextInt(); slove(t); } sc.close(); } public static void slove(int t){ Map<Integer,String> map = new HashMap<>(); map.put(t," "); int num = 0; int k = 0; while (t!=1){ char[] arr = String.valueOf(t).toCharArray(); num = 0; for (int j = 0; j < arr.length; j++) { k = arr[j] - '0'; num+=k*k; } t = num; //如果存在当前key那么就不会得到1,输出false if(map.get(t)!=null){ System.out.println("false"); return; }else { map.put(t," "); } } System.out.println("true"); } }
- 数字和字符串进行归并，每四个数字后边跟一个字母，如果字母多余那么跟在后边
import java.util.*; public class text { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); String s1 = scanner.nextLine(); String s2 = scanner.nextLine(); String[] split1 = s1.split(" "); String[] split2 = s2.split(" "); if (split1.length == 0 && split2.length == 0) { System.out.println(); return; } if (split1.length==0){ System.out.println(s2); return; } if (split2.length==0){ System.out.println(s1); return; } StringBuffer sb = new StringBuffer(); int index = 0; for (int i=0;i<split1.length;i++){ if (i%4 == 3 && index < split2.length){ sb.append(split1[i]).append(" ").append(split2[index++]).append(" "); } else { sb.append(split1[i]).append(" "); } } //成立说明含有字母的序列没有输出完 if (index <= split2.length-1){ for (int i=index;i<split2.length;i++){ sb.append(split2[i]).append(" "); } } System.out.println(sb.toString().trim()); } }
、
import java.util.*; public class Main { public static void main(String[] args) { Scanner sc = new Scanner(System.in); String s = sc.nextLine(); //\\s表示 空格,回车,换行等空白符, //+号表示一个或多个的意思 String[] str = s.split(",\\s+"); Map<Integer, Integer> map = new HashMap<>(); int sum = 0; for (int i = 0; i < str.length; i++) { int value = Integer.valueOf(str[i]); if (map.containsKey(-value) && map.get(-value) > 0) { int count = map.get(-value); map.put(-value, count - 1); sum++; } else { int count = map.getOrDefault(value, 0); map.put(value, count + 1); } } System.out.println(sum); } }
、
- 实现一个数组的最长递增序列
import java.util.*; public class text5 { public static void main(String[] args) { Scanner sc = new Scanner(System.in); String[] str= sc.nextLine().split(" "); int[] arr = new int[str.length]; for (int i = 0; i < str.length; i++){ arr[i] = Integer.parseInt(str[i]); } int max = 0, count = 0, ss = 0, x = 0, y = 0; for (int i = 0; i < str.length - 1; i++) { y = i + 1;//判断是否递增，是的话count++; if (arr[i + 1] > arr[i]) { count++; if (count > max) { max = count; ss = x; } } else { count = 0; x = y;//不连续递增，则索引改变为下一个目标 } } for (int i = ss; i <= ss + max; i++) { if (i == (ss + max)) { System.out.print(arr[i]); } else { System.out.print(arr[i] + " "); } } } }
- 归并排序
import java.util.*; public class Main { public static void main(String[] args) { Scanner sc = new Scanner(System.in); int n = sc.nextInt(); int[] a = new int[n]; for (int i=0;i<n;i++){ a[i] = sc.nextInt(); } int[] sort = sort(a, 0, n - 1); for (int i=0;i<n;i++){ System.out.println(sort[i] + " "); } } public static int[] sort(int[] a,int low,int high){ int mid = (low + high) / 2; if(low < high){ sort(a,low,mid); sort(a,mid+1,high); //左右归并 merge(a,low,mid,high); } return a; } public static void merge(int[] a, int low, int mid, int high) { int[] temp = new int[high-low+1]; int i= low; int j = mid+1; int k=0; // 把较小的数先移到新数组中 while(i<=mid && j<=high){ if(a[i]<a[j]){ temp[k++] = a[i++]; }else{ temp[k++] = a[j++]; } } // 把左边剩余的数移入数组 while(i<=mid){ temp[k++] = a[i++]; } // 把右边边剩余的数移入数组 while(j<=high){ temp[k++] = a[j++]; } // 把新数组中的数覆盖nums数组 for(int x=0;x<temp.length;x++){ a[x+low] = temp[x]; } } }
- 分饼干问题：没个人要达到满意，每个人至少分得一个饼干
import java.util.*; public class Main { public static void main(String [] args) { Scanner sc = new Scanner(System.in); int n = sc.nextInt(); int[] arr = new int[n]; for (int i=0;i<n;i++){ arr[i] = sc.nextInt(); } System.out.println(outCookie(arr)); } public static int outCookie(int[] arr) { if(arr.length <= 0) { return 0; } int[] sum = new int[arr.length]; sum[0] = 1; for(int i = 1;i<sum.length;i++){ sum[i] = 1; if(arr[i] > arr[i-1]){ sum[i] = sum[i-1]+1; } } for(int i = sum.length-2;i>=0;i--){ if(arr[i] > arr[i+1]){ sum[i] = Math.max(sum[i],sum[i+1]+1); } } int num = 0; for(int i = 0;i < arr.length;i++){ num += sum[i]; } return num; } }
- 使用两个栈，使得输出的栈有序
public static Stack<Integer> sortBy2Stack(Stack<Integer> stack){ Stack<Integer> tempStack=new Stack();//结果栈 int j=0; while(stack.size()>0){ //pop:删除此堆栈顶部的对象，并将该对象作为此函数的值返回 int temp=stack.pop(); if(tempStack.size()!=0){//判断结果栈是否为空 //peek:查看此堆栈顶部的对象，而不从堆栈中删除它 while (tempStack.size()>0 && tempStack.peek() > temp){ //push:将项目推送到此堆栈的顶部 stack.push(tempStack.pop()); j++;//记录出栈次数 } //push:将项目推送到此堆栈的顶部 tempStack.push(temp); while(j>0){ //push:将项目推送到此堆栈的顶部 tempStack.push(stack.pop()); j--;//根据出栈次数重新压栈 } }else{ tempStack.push(temp); } } return tempStack; }