Java常用算法
(0)回调
01.定义回调接口和事件
02.实现回调接口
03.在运行类传入回调接口
04.调起类传入 实现的回调接口对象
1.冒泡排序
原理:依次递归，两两交换
int[] ss=new int[]{11,43,45,12,34,45,13,99,9,1}; for (int i = 0; i < ss.length; i++) { for (int j = 0; j <ss.length-1-i ; j++) {//第二次遍历无需涉及上次遍历过的最后位置 if(ss[j]>ss[j+1]){ int s=ss[j];//遍历两两交换 ss[j]=ss[j+1]; ss[j+1]=s; } } }
2.快速排序
原理:选取一个基值，把数小的放在基值左边，大的放在基值右边，如此后再分治递归
if(i<j){ //通过一趟排序获得基值 int pivot = quickSort(array, i, j); //分治递归 partation(array, i, pivot-1); partation(array, pivot+1, j); } private static int quickSort(int[] array,int i, int j) { //一般默认设置基值为首位的值 int pivot = array[i]; while(i<j) { //当基值小于最后一位的值，则将j的值减1，得到第一个比基值小的值，然后覆盖 while(i<j&&array[j]>pivot) { j--; } array[i] = array[j]; //当基值大于第一位的值，则将i的值加1，得到第一个比基值大的值，然后覆盖 while(i<j&&array[i]<pivot) { i++; } array[j] = array[i]; } array[i] = pivot; // 位置换成基值，左边比基值小，右边比基值大 return i; }
3.二分法
原理：每次从最大数和最小数的中小开始往左右遍历，在遍历过程中不断缩小low和high
public static int BinarySearch(int[] array, int T) { int low, high, mid; low = 0; high = array.length - 1; while (low <= high) { mid = (low + high) / 2; //重新计算mid if (array[mid] < T) { low = mid + 1; } else if (array[mid]>T) { high = mid - 1; } else { return mid; } } return -1; }
4.二叉树递归
先序遍历：
1 2 4 8 9 5 3 6 7
中序遍历：
8 4 9 2 5 1 6 3 7
后序遍历：
8 9 4 5 2 6 7 3 1
/** * 先序遍历 * */ public static void preOrderTraverse(Node node) { if (node == null) return; System.out.print(node.data + " "); preOrderTraverse(node.leftChild); preOrderTraverse(node.rightChild); } /** * 中序遍历 * */ public static void inOrderTraverse(Node node) { if (node == null) return; inOrderTraverse(node.leftChild); System.out.print(node.data + " "); inOrderTraverse(node.rightChild); } /** * 后序遍历 * */ public static void postOrderTraverse(Node node) { if (node == null) return; postOrderTraverse(node.leftChild); postOrderTraverse(node.rightChild); System.out.print(node.data + " "); }
5.二叉树非递归
// 先序遍历非递归 public static void preOrder2(BinTree t) { Stack<BinTree> s = new Stack<BinTree>(); while (t != null || !s.empty()) { while (t != null) { System.out.print(t.date); s.push(t); //入栈 t = t.lchild; } if (!s.empty()) { t = s.pop(); //获取出栈元素后出栈 t = t.rchild; } } } // 中序遍历非递归 public static void InOrder2(BinTree t) { Stack<BinTree> s = new Stack<BinTree>(); while (t != null || !s.empty()) { while (t != null) { s.push(t); t = t.lchild; } if (!s.empty()) { t = s.pop(); System.out.print(t.date); t = t.rchild; } } } // 后序遍历非递归 public static void PostOrder2(BinTree t) { Stack<BinTree> s = new Stack<BinTree>(); Stack<Integer> s2 = new Stack<Integer>(); Integer i = new Integer(1); while (t != null || !s.empty()) { while (t != null) { s.push(t); s2.push(new Integer(0)); t = t.lchild; } while (!s.empty() && s2.peek().equals(i)) { s2.pop(); System.out.print(s.pop().date); } if (!s.empty()) { s2.pop(); s2.push(new Integer(1)); t = s.peek(); t = t.rchild; } } }
302
public String firstRequest(String url) throws IOException { System.out.println("访问地址:" + url); URL serverUrl = new URL(url); HttpURLConnection conn = (HttpURLConnection) serverUrl .openConnection(); conn.setRequestMethod("GET"); // 必须设置false，否则会自动redirect到Location的地址 conn.setInstanceFollowRedirects(false); conn.addRequestProperty("Accept-Charset", "UTF-8;"); conn.addRequestProperty("User-Agent", "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:49.0) Gecko/20100101 Firefox/49.0"); conn.addRequestProperty("Referer", "http://jenkins.rnd.meizu.com/login?from=%2F"); conn.connect(); System.out.println(conn.getHeaderField(7));//根据返回header中key组数，获取登录cookie String[] cookies = conn.getHeaderField(7).split("\\;"); String cookie = cookies[0]; String location = conn.getHeaderField("Location"); serverUrl = new URL(location); conn = (HttpURLConnection) serverUrl.openConnection(); conn.setRequestMethod("GET"); conn.addRequestProperty("Accept-Charset", "UTF-8;"); conn.addRequestProperty("User-Agent", "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:49.0) Gecko/20100101 Firefox/49.0"); conn.addRequestProperty("Referer", "http://jenkins.rnd.meizu.com/login?from=%2F"); conn.connect(); System.out.println("跳转地址:" + location); return (cookie); }
