zoukankan      html  css  js  c++  java
  • USACO2.1.3Sorting a ThreeValued Sequence

    Sorting a Three-Valued Sequence 
    IOI'96 - Day 2

    Sorting is one of the most frequently performed computational tasks. Consider the special sorting problem in which the records to be sorted have at most threedifferent key values. This happens for instance when we sort medalists of a competition according to medal value, that is, gold medalists come first, followed by silver, and bronze medalists come last.

    In this task the possible key values are the integers 1, 2 and 3. The required sorting order is non-decreasing. However, sorting has to be accomplished by a sequence of exchange operations. An exchange operation, defined by two position numbers p and q, exchanges the elements in positions p and q.

    You are given a sequence of key values. Write a program that computes the minimal number of exchange operations that are necessary to make the sequence sorted.

    PROGRAM NAME: sort3

    INPUT FORMAT

    Line 1: N (1 <= N <= 1000), the number of records to be sorted
    Lines 2-N+1: A single integer from the set {1, 2, 3}

    SAMPLE INPUT (file sort3.in)

    9
    2
    2
    1
    3
    3
    3
    2
    3
    1
    

    OUTPUT FORMAT

    A single line containing the number of exchanges required

    SAMPLE OUTPUT (file sort3.out)

    4
    

     题解:贪心。方法非常的简单,先分别统计出1,2,3的各自个数,假设分别有,a,b,c个,然后从1扫描到a,遇到3就从n倒过来扫描,找到1就交换,遇见2就从a+1扫描到n,找到1和它交换。上述步骤执行完,这时1已经是有序的了。现在只要从a+b+1扫描到n,遇见2就从a+1开始扫描,找到3交换。结束之后序列就是有序的了。

    View Code
     1 /*
     2 ID:spcjv51
     3 PROG:sort3
     4 LANG:C
     5 */
     6 #include<stdio.h>
     7 void swap(int *x,int *y)
     8 {
     9     int temp;
    10     temp=*x;
    11     *x=*y;
    12     *y=temp;
    13 }
    14 int main(void)
    15 {
    16     freopen("sort3.in","r",stdin);
    17     freopen("sort3.out","w",stdout);
    18     int n,a,b,c,i,j,ans;
    19     int f[1005];
    20     scanf("%d",&n);
    21     memset(f,0,sizeof(f));
    22     a=0;
    23     b=0;
    24     c=0;
    25     ans=0;
    26     for(i=1; i<=n; i++)
    27     {
    28         scanf("%d",&f[i]);
    29         if(f[i]==1)a++;
    30         if(f[i]==2)b++;
    31         if(f[i]==3)c++;
    32     }
    33 
    34 for(i=1; i<=a; i++)
    35     {
    36         while(f[i]==1)i++;
    37         if(f[i]==3)
    38         {
    39             for(j=n;j>=0; j--)
    40              if(f[j]==1)
    41             {
    42                 swap(&f[i],&f[j]);
    43                 ans++;
    44                 break;
    45             }
    46         }
    47         if(f[i]==2)
    48         {
    49             for(j=a+1; j<=n; j++)
    50             if(f[j]==1)
    51             {
    52                 swap(&f[i],&f[j]);
    53                 ans++;
    54                 break;
    55             }
    56 
    57         }
    58 
    59     }
    60 for(i=n-c+1; i<=n; i++)
    61     {
    62         while(f[i]==3)i++;
    63             for(j=a+1; j<=n-c; j++)
    64             if (f[j]==3)
    65             {
    66                 swap(&f[i],&f[j]);
    67                 ans++;
    68                 break;
    69             }
    70 
    71     }
    72 printf("%d\n",ans);
    73 return 0;
    74 }
  • 相关阅读:
    用GDB调试程序(一)
    vim添加删除多行注释
    python binary lib on win/各种python库的二进制包
    python使用libssh2连接linux
    python xpath
    splinter python浏览器自动化操作,模拟浏览器的行为
    pytesser图片文本识别
    python验证码识别
    Python 之 使用 PIL 库做图像处理
    Connection reset by peer问题分析
  • 原文地址:https://www.cnblogs.com/zjbztianya/p/2890504.html
Copyright © 2011-2022 走看看