3.12美团笔试解法
1
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
int n = scanner.nextInt();
for (int i = 0; i < n; i++) {
int num = scanner.nextInt();
if (isNum(num)) {
System.out.println("yes");
}else {
System.out.println("no");
}
}
}
private static boolean isNum(int num) {
if (num % 11 == 0) {
return true;
}
int count = 0;
while (num != 0) {
if (num % 10 == 1) {
count ++;
}
num /= 10;
}
return count >= 2;
}
} 2
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
int n = scanner.nextInt();
int[] nums = new int[n];
for (int i = 0; i < n; i++) {
nums[i] = scanner.nextInt();
}
int[] preSum = getPreSum(nums);
int count = 0;
for (int i = 0; i < n; i++) {
for (int j = i; j < n; j++) {
// [i, j]
if ((preSum[j + 1] - preSum[i]) % 2 == 0) {
count ++;
}
}
}
System.out.println(count);
}
private static int[] getPreSum(int[] nums) {
// res[i] [0,i-1]之间的-1的个数
int[] res = new int[nums.length + 1];
for (int i = 0; i < nums.length; i++) {
res[i + 1] = res[i];
if (nums[i] == -1) {
res[i + 1] ++;
}
}
return res;
}
} 3
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
int n = scanner.nextInt();
int m = scanner.nextInt();
int[][] nums = new int[n][2];
for (int i = 0; i < n; i++) {
nums[i][0] = scanner.nextInt();
nums[i][1] = scanner.nextInt();
}
boolean[] visited = new boolean[m + 1];
Arrays.fill(visited, false);
int res = fun(nums, n - 1, visited);
System.out.println(res);
}
/**
* 下一个尝试满足的顾客下表 [0,n-1]
*/
public static int fun(int[][] nums, int i, boolean[] used) {
if (i < 0) {
return 0;
}
// 不满足当前顾客
int res = fun(nums, i - 1, used);
// 满足当前顾客
int[] customer = nums[i];
if (!used[customer[0]] && !used[customer[1]]) {
used[customer[0]] = true;
used[customer[1]] = true;
res = Math.max(res, fun(nums, i - 1, used) + 1);
used[customer[0]] = false;
used[customer[1]] = false;
}
return res;
}
} 4
import java.util.*;
public class Main {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
int n = scanner.nextInt();
int m = scanner.nextInt();
int[] nums = new int[m];
for (int i = 0; i < nums.length; i++) {
nums[i] = scanner.nextInt();
}
int res = fun(nums, n);
System.out.println(res);
}
private static int fun(int[] times, int n) {
Map<Integer, List<Integer>> map = new HashMap<>();
for (int i = 1; i <= n; i++) {
map.put(i, new ArrayList<>());
}
for (int i = 1; i < times.length; i++) {
List<Integer> list = map.get(times[i]);
list.add(i);
}
int curPos = 1;
int count = 0;
for (int i = 0; i + 1 < times.length; i++) {
if (times[i + 1] == curPos) {
// 当前所在节点下一秒爆炸，找到下一个最晚爆炸的点
int maxIndex = -1;
int maxValue = 0;
for (int j = 1; j <= n; j++) {
List<Integer> list = map.get(j);
if (list.isEmpty()) {
maxIndex = j;
maxValue = Integer.MAX_VALUE;
break;
}
int k = 0;
for (; k < list.size() && list.get(k) <= i; k++) {
}
if (k == list.size()) {
maxIndex = j;
maxValue = Integer.MAX_VALUE;
}else {
Integer time = list.get(k);
if (time > maxValue) {
maxIndex = j;
maxValue = time;
}
}
}
// 删除所有maxValue之前的时间
curPos = maxIndex;
count ++;
// // 移除<=maxValue的所有时间
// for (int j = 1; j <= n; j++) {
// List<Integer> list = map.get(j);
// Iterator<Integer> iterator = list.iterator();
// while (iterator.hasNext()) {
// if (iterator.next() <= maxValue) {
// iterator.remove();
// }
// }
// }
}
}
return count;
}
} 5
import javax.swing.tree.TreeNode;
import java.util.*;
public class Main {
public static class TreeNode {
int val;
List<TreeNode> children = new ArrayList<>();
public TreeNode(int val) {
this.val = val;
}
}
private static int white = 0;
private static int black = 0;
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
int nodes = scanner.nextInt();
int[] colors = new int[nodes];
int[] parents = new int[nodes];
for (int i = 0; i < colors.length; i++) {
colors[i] = scanner.nextInt();
}
for (int i = 0; i < parents.length; i++) {
parents[i] = scanner.nextInt();
}
TreeNode root = toTree(parents);
white = 0;
black = 0;
dfs(root, colors);
System.out.println(white + " " + black);
}
/**
* root不为空
*/
private static void dfs(TreeNode root, int[] colors) {
int color = colors[root.val - 1];
if (color == 0) {
// 白色
int count = 0;
if (root.children.isEmpty()) {
count = 1;
}else {
for (TreeNode child : root.children) {
if (colors[child.val - 1] == 1) {
count = 1;
break;
}
}
}
white += count;
}else {
// 黑色
int count = 0;
if (root.children.isEmpty()) {
count = 1;
}else {
count = 1;
for (TreeNode child : root.children) {
if (colors[child.val - 1] != 0) {
count = 0;
break;
}
}
}
black += count;
}
for (TreeNode child : root.children) {
dfs(child, colors);
}
}
public static TreeNode toTree(int[] parents) {
Map<Integer, TreeNode> map =new HashMap<>();
TreeNode root = new TreeNode(-1);
for (int i = 0; i < parents.length; i++) {
if (parents[i] == 0) {
root.val = i + 1;
map.put(i + 1, root);
}
}
for (int i = 0; i < parents.length; i++) {
int child = i + 1;
int parent = parents[i];
TreeNode parentNode = map.computeIfAbsent(parent, v -> new TreeNode(v));
TreeNode childNode = map.computeIfAbsent(child, v -> new TreeNode(v));
parentNode.children.add(childNode);
}
return root;
}
} 
就算你真拿到牛友也会为你开心的