蓝桥日记③2016第七届省赛（软件类）JavaA组✿答案解析
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【蓝桥日记③】2016第七届省赛（软件类）JavaA组✿答案解析
文章目录
官网题库中搜索相应题目
1、煤球数目
考点：找规律，模拟求和
package sevenSession;
/*** 2016第七届 1、煤球数目 ***/
public class test1
public static void main(String[] args)
int pre = 1, res = 1;
for (int i = 2; i <= 100; i++)
pre += i;
res += pre;
System.out.println(res);
答案：
171700
2、生日蜡烛
考点：暴力枚举
package sevenSession;
/*** 2016第七届 2、生日蜡烛 ***/
public class test2
public static void main(String[] args)
int candles = 236, begin = 0;
for (int j = 1; j <= 100; j++)
int k = j, sum = 0;
while (sum < candles)
sum += k;
k += 1;
if (sum == candles)
begin = j;
break;
System.out.println(begin);
答案：
26
3、搭积木
考点：全排列
package sevenSession;
/*** 2016第七届 3、搭积木 ***/
public class test3
static int res;
public static void main(String[] args)
int[] a = 0, 1, 2, 3, 4, 5, 6, 7, 8, 9;
res = 0;
backtrack(a, 0, a.length);
System.out.println(res);
static private void backtrack(int[] a, int begin, int end)
if (begin == end)
if (check(a)) res++;
return;
for (int i = begin; i < end; i++)
int t = a[i]; a[i] = a[begin]; a[begin] = t;
backtrack(a, begin + 1, end);
t = a[i]; a[i] = a[begin]; a[begin] = t;
static private boolean check(int[] a)
if (a[0] > a[1] || a[0] > a[2]) return false;
if (a[1] > a[3] || a[1] > a[4]) return false;
if (a[2] > a[4] || a[2] > a[5]) return false;
if (a[3] > a[6] || a[3] > a[7]) return false;
if (a[4] > a[7] || a[4] > a[8]) return false;
if (a[5] > a[8] || a[5] > a[9]) return false;
return true;
答案：
768
4、分小组
考点：排列组合
package sevenSession;
/*** 2016第七届 4、分小组 ***/
public class test4
public static String remain(int[] a)
String s = "";
for (int i = 0; i < a.length; i++)
if (a[i] == 0) s += (char) (i + 'A');
return s;
public static void f(String s, int[] a)
for (int i = 0; i < a.length; i++)
if (a[i] == 1) continue;
a[i] = 1;
for (int j = i + 1; j < a.length; j++)
if (a[j] == 1) continue;
a[j] = 1;
for (int k = j + 1; k < a.length; k++)
if (a[k] == 1) continue;
a[k] = 1;
if (k == 3)
System.out.println(s + " " + (char)(i + 'A') + (char)(j + 'A') + (char)(k + 'A') + " " + remain(a));
a[k] = 0;
a[j] = 0;
a[i] = 0;
public static void main(String[] args)
int[] a = new int[9];
a[0] = 1;
for (int b = 1; b < a.length; b++)
a[b] = 1;
for (int c = b + 1; c < a.length; c++)
a[c] = 1;
String s = "A" + (char) (b + 'A') + (char) (c + 'A');
f(s, a);
a[c] = 0;
a[b] = 0;
答案：
System.out.println(s + " " + (char)(i + 'A') + (char)(j + 'A') + (char)(k + 'A') + " " + remain(a));
5、抽签
考点：排列组合+递归
package sevenSession;
/*** 2016第七届 5、抽签 ***/
public class test5
public static void f(int[] a, int k, int n, String s)
if (k == a.length)
if (n == 0) System.out.println(s);
return;
String s2 = s;
for (int i = 0; i <= a[k]; i++)
f(a, k + 1, n - i, s2);
s2 += (char) (k + 'A');
public static void main(String[] args)
int[] a = 4, 2, 2, 1, 1, 3;
f(a, 0, 5, "");
答案：
f(a, k + 1, n - i, s2);
6、寒假作业
考点：排列组合
package sevenSession;
/*** 2016第七届 6、剪邮票 ***/
public class test6
static int res;
public static void main(String[] args)
int[] a = new int[13];
for (int i = 1; i <= 13; i++) a[i - 1] = i;
res = 0;
backtrack(a, 0, 13);
System.out.println(res);
static private void backtrack(int[] a, int begin, int end)
if (begin == end && check(a))
res++;
return;
for (int i = begin; i < end; i++)
int t = a[begin]; a[begin] = a[i]; a[i] = t;
backtrack(a, begin + 1, end);
t = a[begin]; a[begin] = a[i]; a[i] = t;
static private boolean check(int[] a)
return a[0] + a[1] == a[2] && a[3] - a[4] == a[5] &&
a[6] * a[7] == a[8] && (a[9] % a[10] == 0 && a[9] / a[10] == a[11]);
答案：
64
7、剪邮票
考点：组合问题+DFS
package sevenSession;
import java.util.ArrayDeque;
import java.util.Queue;
/*** 2016第七届 7、剪邮票 ***/
public class test7
static int res = 0;
public static void main(String[] args)
int[] a = new int[12];
backtrack(a, 0, 12, 5);
System.out.println(res);
static private void backtrack(int[] a, int begin, int end, int k)
if (end - begin + 1 < k) return;
if (k == 0)
if(check(a)) res++;
for (int i = begin; i < end; i++)
a[i] = 1;
backtrack(a, i + 1, end, k - 1);
a[i] = 0;
static private boolean check(int[] a)
Queue<int[]> queue = new ArrayDeque<>();
boolean[] mark = new boolean[12];
for (int i = 0; i < 12; i++)
if (a[i] == 1)
queue.offer(new int[]i / 4, i % 4);
mark[i] = true;
break;
if (queue.isEmpty()) return false;
int cnt = 1;
int[] dirs = -1, 0, 1, 0, -1;
while (!queue.isEmpty())
int[] cur = queue.poll();
for (int i = 0; i < 4; i++)
int x = cur[0] + dirs[i], y = cur[1] + dirs[i + 1];
int xy = x * 4 + y;
if (x < 0 || y < 0 || x >= 3 || y >= 4) continue;
if (a[xy] == 0 || mark[xy]) continue;
queue.offer(new int[]x, y);
mark[xy] = true;
cnt++;
return cnt == 5;
答案：
116
8、取球博弈
考点：博弈+记忆化搜索
package sevenSession;
import java.util.Arrays;
import java.util.Scanner;
/*** 2016第七届 8、取球博弈 ***/
public class test8
static int[] ns = new int[3];
static char[][][] cache = new char[1000][2][2];
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