题目链接：戳我
题目大意：
给定一个n，则对应一个长度 2n-1 数组，此数组前 n个数全为 n, 最后一个数必须是24，即 第 2n-1 个数是24。
通过把这n个数加减乘除，每个数都必须用一次，且只能一次，并且运算完的数也都得用一次。也就是做n-1次。
输出过程 xi ? xj 第 i 个数与第 j 个数做 ? 运算 这种形式
样例解释：
4 n = 4 即(a[1]=4,a[2]=4,a[3]=4,a[4]=4)
1 * 2 表示 (a[5] = a[\1] * a[\2] = 16)
5 + 3 表示 (a[6] = a[5] + a[3] = 20)
6 + 4 表示 (a[7] = a[6] + a[4] = 24)
每个数都用了一次，且是 n - 1 次运算，每次运算的数均用上了
解题思路：
官方题解：
代码
//Author LJH
//www.cnblogs.com/tenlee
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cctype>
#include <cmath>
#include <algorithm>
#include <vector>
#include <queue>
#include <stack>
#include <map>
#define clc(a, b) memset(a, b, sizeof(a))
using namespace std;
const int inf = 0x3f;
const int INF = 0x3f3f3f3f;
const int maxn = 1e5+5;
int n;
void n15()
{
int i;
printf("1 + 2
");
for(i = 1; i < 2; i++)
{
printf("%d + %d
", n+i, i+2);
}
printf("%d / 4
", n+2); //n+3 = 3
printf("5 + 6
"); // n + 4
for(i = 7;i <= 12; i++)
{
printf("%d + %d
", i, n+i-3);
}
printf("%d / %d
", n+10, 13); //n+11 8
printf("%d * %d
", n+3, n+11); //n+12 3*8
printf("14 - 15
");//n+13
for(i = n+14; i <= 2*n-2; i++)
{
printf("%d * %d
", i-n+2, i-1);
}
printf("%d + %d
", n+12, 2*n-2);
}
void n13()
{
int i;
printf("1 + 2
");
for(i = 1; i < 2; i++)
{
printf("%d + %d
", n+i, i+2);
}
printf("%d / 4
", n+2); //n+3 = 3
printf("5 + 6
"); // n + 4
for(i = 7;i <= 12; i++)
{
printf("%d + %d
", i, n+i-3);
}
printf("%d / %d
", n+10, 13); //n+11 8
printf("%d * %d
", n+3, n+11); //n+12 3*8
}
void n14()
{
puts("1 + 2"); //15 2*14
puts("3 / 4"); //16 1
puts("5 / 6"); //17 1
puts("16 + 17");//18 2
puts("7 / 8"); //19 1
puts("9 / 10"); //20 1
puts("19 + 20"); //21 2
puts("18 + 21");//22 4
puts("15 - 22"); //23 24
puts("11 - 12");//24 0
puts("13 - 14"); //25 0
puts("24 + 25"); //26 0
puts("26 + 23");// 27
}
void n4()
{
printf("1 * 2
");
printf("3 + 5
");
printf("4 + 6
");
}
void n5()
{
printf("1 / 2
");
printf("6 / 3
");
printf("4 - 7
");
printf("5 * 8
");
}
void n6()
{
printf("1 * 2
");
printf("7 - 3
");
printf("8 - 4
");
printf("9 - 5
");
printf("10 + 6
");
}
void n7()
{
printf("1 * 2
");
printf("3 / 4
");
printf("5 + 6
");
printf("8 - 9
");
printf("11 / 10
");
printf("12 * 7
");
}
void n8()
{
printf("1 + 2
");
printf("3 + 9
");
printf("4 - 5
");
printf("6 * 11
");
printf("7 * 12
");
printf("8 * 13
");
printf("10 + 14
");
}
void n9()
{
printf("1 + 2
");
printf("3 + 10
");
printf("4 / 5
");
printf("6 / 7
");
printf("8 / 9
");
printf("11 - 12
");
printf("15 - 13
");
printf("16 - 14
");
}
void n10()
{
puts("1 + 2"); //11 20
puts("3 / 4");//12 1
puts("5 / 6");// 13 1
puts("7 / 8");//14 1
puts("9 / 10");//15 1
puts("11 + 12");//16 21
puts("16 + 13");//17 22
puts("17 + 14");//18 23
puts("18 + 15");//18 24
}
void n11()
{
puts("1 + 2"); //12 22
puts("12 / 3"); //13 2
puts("4 + 5");//14 22
puts("14 + 13"); //15 24
puts("6 - 7");//16 0
puts("8 - 9"); //17 0
puts("10 - 11"); // 18 0
puts("16 * 17");//19
puts("18 * 19");//20
puts("20 + 15");//21
}
void n12()
{
puts("1 + 2"); // 13 24
puts("3 - 4"); // 14
puts("14 * 5"); //15
puts("15 * 6"); //16
puts("16 * 7");//17
puts("17 * 8");//18
puts("18 * 9");//19
puts("19 * 10");//20
puts("20 * 11");//21
puts("21 * 12");//22
puts("22 + 13");//23
}
int main()
{
while(~scanf("%d", &n))
{
if(n < 4)
{
puts("-1");
continue;
}
if(n == 4) n4();
else if(n == 5) n5();
else if(n == 6) n6();
else if(n == 7) n7();
else if(n == 8) n8();
else if(n == 9) n9();
else if(n == 10) n10();
else if(n == 11) n11();
else if(n == 12) n12();
else if(n == 13) n13();
else if(n == 14) n14();
else
{
n15();
}
}
}
标程
#include<iostream>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<cstdio>
using namespace std;
int n;
int main(){
// freopen("data.in","r",stdin);
// freopen("dataa.out","w",stdout);
while (scanf("%d",&n)!=EOF){
if (n>=15){
printf("1 + 2
"); printf("3 + 4
"); printf("5 + 6
"); printf("7 + 8
"); printf("%d + 9
",n+1);
printf("%d / 10
",n+2); printf("%d / 11
",n+3); printf("%d / 12
",n+4); printf("%d / 13
",n+5);
printf("%d * %d
",n+6,n+7); printf("%d * %d
",n+8,n+9); printf("%d * %d
",n+10,n+11); printf("14 - 15
");
int now=n+13; for (int i=16;i<=n;i++){printf("%d * %d
",i,now); now++;} printf("%d + %d
",n+12,now); continue;
}
if (n>=12){
printf("1 + 2
");
for (int i=1;i<=n*2-24;i++) printf("%d / %d
",i*2+1,i*2+2); int num=n*4-46;
int now=n+1+n*2-24;
if (n!=12){
printf("%d - %d
",n+1,n+2); now++;
for (int i=2;i<=n*2-24;i++){printf("%d - %d
",now,n+1+i); now++;}
}
int k1=now;
printf("%d - %d
",num+1,num+2); num+=3; now++;
for (int i=num;i<=n;i++){printf("%d * %d
",i,now); now++;}
printf("%d + %d
",k1,now); continue;
}
if (n>=10){
printf("1 + 2
");
for (int i=1;i<=24-n*2;i++) printf("%d / %d
",1+2*i,2+2*i);
printf("%d + %d
",n+1,n+2); int now=n+26-n*2;
for (int i=2;i<=24-n*2;i++) {printf("%d + %d
",n+1+i,now); now++;}
if (n==10) continue;
printf("7 - 8
"); printf("17 * 9
"); printf("18 * 10
"); printf("19 * 11
"); printf("20 + 16
"); continue;
}
if (n==9){
printf("1 + 2
"); printf("3 + 10
"); printf("4 / 5
"); printf("6 / 7
"); printf("8 / 9
");
printf("11 - 12
"); printf("15 - 13
"); printf("16 - 14
"); continue;
}
if (n==8){
printf("1 + 2
"); printf("3 + 9
"); printf("4 - 5
"); printf("6 * 11
"); printf("7 * 12
");
printf("8 * 13
"); printf("10 + 14
"); continue;
}
if (n==7){
printf("1 * 2
"); printf("3 / 4
"); printf("5 + 6
"); printf("8 - 9
"); printf("11 / 10
"); printf("12 * 7
"); continue;
}
if (n<=3){printf("-1
"); continue;}
if (n==6){
printf("1 * 2
"); printf("7 - 3
"); printf("8 - 4
"); printf("9 - 5
"); printf("10 + 6
"); continue;
}
if (n==5){
printf("1 / 2
"); printf("6 / 3
"); printf("4 - 7
"); printf("5 * 8
"); continue;
}
if (n==4){
printf("1 * 2
"); printf("3 + 5
"); printf("4 + 6
"); continue;
}
}
return 0;
}