1.带头冲锋(美团)
马拉松项目,超过出发时排在自己前面的任何一个人即可得到表扬,问一共多少人得到表扬?
输入第一行,n,选手数量
输入第二行包括n个正整数,是一个1-n的排列A,表示出发顺序,A[i]表示第i个出发选手的编号。
输入第三行同样包括1-n的排列,表示到达顺序,B[i]表示达到选手的编号。
输入
5
5 3 1 4 2
2 4 5 1 3
输出
3
//思路:用HashSet接收到达选手,每个到达选手分别查看自己身后有没有
// 出发前在自己之前的选手,有的话则+1
import java.util.*;
public class T2 {
public static void main(String[] args) {
Scanner sc= new Scanner(System.in);
int n = sc.nextInt();
int[] A = new int[n];
int[] B = new int[n];
for (int i = 0; i < n; i++) {
A[i]=sc.nextInt();
}
Set behand = new HashSet<>(n);
for (int i = 0; i < n; i++) {
B[i]=sc.nextInt();
behand.add(B[i]);
}
int result = 0;
for (int i = 0; i <n ; i++) {
int p =B[i];
behand.remove(p);
for (int j : A) {
if(j==p){
break;
}
//思路:每个到达选手查看自己身后有没有出发前在自己之前的选手
else if(behand.contains(j)){
result++;
break;
}
}
}
System.out.println(result);
}
}
2.数独(华为)
1.判断能否为有效的数独
输入二维数组
[["5","3",".",".","7",".",".",".","."],
["6",".",".","1","9","5",".",".","."],
[".","9","8",".",".",".",".","6","."],
["8",".",".",".","6",".",".",".","3"],
["4",".",".","8",".","3",".",".","1"],
["7",".",".",".","2",".",".",".","6"],
[".","6",".",".",".",".","2","8","."],
[".",".",".","4","1","9",".",".","5"],
[".",".",".",".","8",".",".","7","9"]]
class Solution {
public boolean isValidSudoku(char[][] board) {
int[][] rows = new int[9][9];
int[][] col = new int[9][9];
int[][] sbox = new int[9][9];
for (int i = 0; i < board.length; i++) {
for (int j = 0; j < board[0].length; j++) {
if (board[i][j]!='.'){
//value=1-->9;index=0-->8,所以num需要减1
int num = (int)(board[i][j] - '1');
int index_box = (i/3)*3+j/3;
if (rows[i][num]==1) { return false;}
//如果该行num出现过一次,即重复出现,不成立,否则num第一次出现,num=1;
else { rows[i][num]=1; }
if (col[j][num]==1) { return false;}
else { col[j][num]=1; }
if (sbox[index_box][num]==1) { return false;}
else { sbox[index_box][num]=1; }
}
}
}
return true;
}
}
2.解数独
输入
{5,0,0,6,0,2,0,0,0}
{0,0,8,0,7,0,2,0,0}
...................
{9,0,0,0,0,3,0,0,1}
输出
{5,0,0,6,0,2,0,0,0}
{0,0,8,0,7,0,2,0,0}
...................
{9,0,0,0,0,3,0,0,1}
输入
{5,0,0,6,0,2,0,0,0}
{0,0,8,0,7,0,2,0,0}
...................
{9,0,0,0,0,3,0,0,1}
输出
{5,0,0,6,0,2,0,0,0}
{0,0,8,0,7,0,2,0,0}
...................
{9,0,0,0,0,3,0,0,1}
import java.util.Scanner;
public class Test2 {
public static void main(String[] args) {
int[][] a = new int[9][9];
Scanner sc = new Scanner(System.in);
for (int i=0;i<9;i++){
String s=sc.nextLine();
s=s.substring(1,s.length()-1);
String[] c=s.split(",");
for (int j=0;j<c.length;j++){
a[i][j]=Integer.parseInt(c[j]);
}
}
sc.close();
boolean[][] cols = new boolean[9][9];
boolean[][] rows= new boolean[9][9];
boolean[][] blocks=new boolean[9][9];
for (int i =0;i<a.length;i++){
for (int j=0;j<a.length;j++){
if(a[i][j]!=0){
int k=i/3*3+j/3;
int val=a[i][j]-1;
rows[i][val]=true;
cols[j][val]=true;
blocks[k][val]=true;
}
}
}
DFS(a, cols,rows,blocks);
for(int i=0;i<9;i++){
System.out.print("{");
for (int j=0;j<8;j++){
System.out.print(a[i][j]+",");
}
System.out.println(a[i][8]+"}");
}
}
public static boolean DFS(int[][] a,boolean[][] cols,boolean[][] rows,boolean[][] blocks){
for (int i=0;i<9;i++){
for (int j =0;j<9;j++){
if (a[i][j]==0){
int k=i/3*3+j/3;
for (int l=0;l<9;l++){
if (!cols[j][l]&&!rows[i][l]&&!blocks[k][l]){
rows[i][l]=cols[j][l]=blocks[k][l]=true;
a[i][j]=1+l;
if (DFS(a,cols,rows,blocks)) return true;
rows[i][l]=cols[j][l]=blocks[k][l]=false;
a[i][j]=0;
}
}
return false;
}
}
}
return true;
}
}
输入
5 0 0 6 0 2 0 0 0
0 0 8 0 7 0 2 0 0
.................
9 0 0 0 0 3 0 0 1
输出
5 0 0 6 0 2 0 0 0
0 0 8 0 7 0 2 0 0
.................
9 0 0 0 0 3 0 0 1
import java.util.Scanner;
public class T3 {
public static void main(String[] args) {
Scanner sc=new Scanner(System.in);
while(sc.hasNextInt()){
int[][]a=new int[9][9];
boolean[][] cols = new boolean[9][9];
boolean[][] rows = new boolean[9][9];
boolean[][] blocks = new boolean[9][9];//九大宫的九个数字
for (int i = 0; i < a.length; i++) {
for (int j = 0; j < a.length; j++) {
a[i][j]=sc.nextInt();
if(a[i][j]!=0){
int k = i/3*3+ j/3;//划分九宫格,这里以行优先,自己也可以列优先
int val=a[i][j]-1;
rows[i][val] = true;
cols[j][val] = true;
blocks[k][val] = true;
}
}
}//数据装载完毕
DFS(a, cols, rows, blocks);
for (int i = 0; i < 9; i++) {
for (int j = 0; j < 8; j++) {
System.out.print(a[i][j]+" ");
}
System.out.println(a[i][8]);
}
}
}
public static boolean DFS(int[][] a,boolean[][] cols,boolean[][] rows,boolean[][] blocks) {
for (int i = 0; i < 9; i++) {
for (int j = 0; j < 9; j++) {
if(a[i][j]==0){
int k=i/3*3+j/3;
for (int l = 0; l < 9; l++) {
if(!cols[j][l]&&!rows[i][l]&&!blocks[k][l]){//l对于的数字l+1没有在行列块中出现
rows[i][l] = cols[j][l] = blocks[k][l] = true;
a[i][j] = 1 + l;//下标加1
if(DFS(a, cols, rows, blocks)) return true;//递进则返回true
rows[i][l] = cols[j][l] = blocks[k][l] = false;//递进失败则回溯
a[i][j] = 0;
}
}
return false;//a[i][j]==0时,l发现都不能填进去
}//the end of a[i][j]==0
}
}
return true;//没有a[i][j]==0,则返回true
}
}
3.优惠券(头条)
拥有n种无门槛优惠券,面值为ai,当一件商品售价>=优惠券时即可使用,你要购买m件商品,每件商品售价为bi,问你最少花费多少钱?
输入
3 4
50 100 200
99 199 200 300
输出
248
import java.util.Scanner;
public class toutiao {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int m=sc.nextInt();
int n=sc.nextInt();
int[] A=new int[m];
int[] B=new int[n];
for (int i=0;i<m;i++){
A[i]=sc.nextInt();
}
sort(A); //将优惠券按从小到大排序
for (int i=0;i<n;i++){
B[i]=sc.nextInt();
}
int res=0;
int temp=0;
for (int i=0;i<n;i++){
for (int j=0;j<m;j++){
//从小到大搜索最合适的优惠券,差值最小且大于0时最合适
if (B[i]-A[j]>=0&&B[i]-A[j]<=B[i]-A[0]){
temp=B[i]-A[j];
}
}
res=res+temp;
}
System.out.println(res);
}
//冒泡排序
public static int[] sort(int[] arr){
for(int i = 0;i<arr.length-1;i++){
for(int j= 0;j<arr.length-1-i;j++){
if(arr[j]>arr[j+1]){
int temp = arr[j];
arr[j] = arr[j+1];
arr[j+1] = temp;
}
}
}
return arr;
}
}