//乱序
public static void luan(int[] arr){
for(int i=0;i<arr.length;i++){
int random = (int)(Math.random()*(arr.length-i-1));
int temp = arr[arr.length -i-1];
arr[arr.length -i-1] = arr[random];
arr[random] = temp;
}
for (int i : arr) {
System.out.println(i);
}
}
//View Group个数
public int count1(View view) {
int count = 0;
if (view == null) {
return 0;
}
if (view instanceof ViewGroup) {
count++;
ViewGroup group = (ViewGroup) view;
for (int i = 0; i < group.getChildCount(); i++) {
View child = group.getChildAt(i);
if (child instanceof ViewGroup) {
count += count1(child);
} else {
count++;
}
}
}
return count;
}
//View Group个数
public int count2(View view) {
int count = 0;
if (null == view) {
return 0;
}
if (view instanceof ViewGroup) {
ViewGroup group = (ViewGroup) view;
LinkedList<ViewGroup> quene = new LinkedList<>();
quene.add(group);
while (!quene.isEmpty()) {
ViewGroup viewGroup = quene.removeFirst();
count++;
for (int i = 0; i < viewGroup.getChildCount(); i++) {
View child = viewGroup.getChildAt(i);
if (child instanceof ViewGroup) {
quene.add((ViewGroup) child);
} else {
count++;
}
}
}
}
return count;
}
//前序遍历
public void recursivePreOrder(TreeNode p) {
if (p == null) {
return;
}
System.out.println(p.val);
recursivePreOrder(p.left);
recursivePreOrder(p.right);
}
// 前序
public void recursivePreOrder1(TreeNode p) {
if (p == null) {
return;
}
Stack<TreeNode> treeNodes = new Stack<>();
treeNodes.push(p);
while (!treeNodes.empty()) {
TreeNode node = treeNodes.pop();
System.out.println(node.val);
if (p.right != null) {
treeNodes.push(p.right);
}
if (p.left != null) {
treeNodes.push(p.left);
}
}
}
//中序
public void mid(TreeNode p) {
if (p == null) {
return;
}
Stack<TreeNode> stacks = new Stack<>();
while (!stacks.empty() || p != null) {
while (p != null) {
stacks.push(p);
p = p.left;
}
p = stacks.pop();
System.out.println(p.val);
p = p.right;
}
}
//后序
public void after(TreeNode p) {
if (p == null) {
return;
}
Stack<TreeNode> stacks = new Stack<>();
TreeNode pre = null;
while (!stacks.empty() || p != null) {
while (p != null) {
stacks.push(p);
p = p.left;
}
TreeNode right = stacks.peek().right;
if (right == null || right == pre) {
//如果又节点为空 或者有节点已经被访问过
stacks.pop();
System.out.println(p.val);
pre = p;
p = null;
} else {
p = p.right;
}
}
}
//后序
public void after1(TreeNode p) {
if (p == null) {
return;
}
Stack<TreeNode> stacks = new Stack<>();
List<Integer> list = new ArrayList<>();
stacks.push(p);
while (!stacks.empty()) {
TreeNode cur = stacks.pop();
list.add(0, cur.val);
if (cur.left != null) {
stacks.push(cur.left);
}
if (cur.right != null) {
stacks.push(cur.right);
}
}
System.out.println(list);
}
//层级排序
public void levelOrder(TreeNode node) {
List<List<Integer>> list = new ArrayList<>();
LinkedList<TreeNode> quene = new LinkedList<>();
quene.add(node);
while (!quene.isEmpty()) {
LinkedList<Integer> temp = new LinkedList<>();
for (int i = 0; i < quene.size(); i++) {
TreeNode poll = quene.poll();
temp.add(poll.val);
if (node.left != null) {
quene.add(node.left);
}
if (node.right != null) {
quene.add(node.right);
}
}
list.add(temp);
}
}
public class TreeNode {
int val;
TreeNode left;
TreeNode right;
TreeNode(int x) {
val = x;
}
}
//棧實現隊列
public class stackQuene {
Stack<Integer> stack = new Stack<>();
Stack<Integer> stack1 = new Stack<>();
public void push(Integer i) {
stack.add(i);
}
public void pop() {
if (stack.size() != 0) {
while (!stack.isEmpty()) {
int temp = stack.pop();
stack1.push(temp);
}
}
stack1.pop();
}
}
public int getN(int n) {
if (n == 1) {
return 1;
}
if (n == 2) {
return 2;
}
return getN(n - 1) + getN(n - 2);
}
//上樓梯
public int getN1(int n) {
if (n == 1) {
return 1;
}
if (n == 2) {
return 2;
}
int temp1 = 1;
int temp2 = 2;
int res = 0;
for (int i = 3; i <= n; i++) {
res = temp1 + temp2;
temp1 = temp2;
temp2 = res;
}
return res;
}
//二分法 在array中查找n
public int sum(int[] array, int n) {
int start = 0;
int end = array.length;
int mid;
while (start <= end) {
mid = start + (end - start) / 2;
if (array[mid] == n) {
return mid;
} else if (n > array[mid]) {
start = mid + 1;
} else {
end = mid - 1;
}
}
return -1;
}
//链表求和
public ListNode sumNode(ListNode node1, ListNode node2) {
ListNode head = null;
ListNode res = null;
int carry = 0;
while (node1 != null | node2 != null) {
int n1 = node1 == null ? 0 : node1.val;
int n2 = node2 == null ? 0 : node2.val;
int sum = n1 + n2 + carry;
if (head == null) {
res = head = new ListNode(sum % 10);
} else {
head.next = new ListNode(sum % 10);
head = head.next;
}
carry = sum/10;
if(node1!=null){
node1 = node1.next;
}
if(node2!=null){
node2 = node2.next;
}
}
if(carry!=0){
head.next = new ListNode(carry);
}
return res;
}
public class ListNode {
int val;
ListNode next;
ListNode() {
}
ListNode(int val) {
this.val = val;
}
ListNode(int val, ListNode next) {
this.val = val;
this.next = next;
}
}
面试总结 算法02
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