码迷,mamicode.com
首页 > 其他好文 > 详细

poj 3356

时间:2015-08-16 21:32:50      阅读:102      评论:0      收藏:0      [点我收藏+]

标签:

Description

Let x and y be two strings over some finite alphabet A. We would like to transform x into y allowing only operations given below:

  • Deletion: a letter in x is missing in y at a corresponding position.
  • Insertion: a letter in y is missing in x at a corresponding position.
  • Change: letters at corresponding positions are distinct

Certainly, we would like to minimize the number of all possible operations.

Illustration

A G T A A G T * A G G C 
| | |       |   |   | |

A G T * C * T G A C G C

Deletion: * in the bottom line
Insertion: * in the top line
Change: when the letters at the top and bottom are distinct

This tells us that to transform x = AGTCTGACGC into y = AGTAAGTAGGC we would be required to perform 5 operations (2 changes, 2 deletions and 1 insertion). If we want to minimize the number operations, we should do it like

A  G  T  A  A  G  T  A  G  G  C 
|  |  |        |     |     |  |

A  G  T  C  T  G  *  A  C  G  C

and 4 moves would be required (3 changes and 1 deletion).

In this problem we would always consider strings x and y to be fixed, such that the number of letters in x is m and the number of letters in y is n where nm.

Assign 1 as the cost of an operation performed. Otherwise, assign 0 if there is no operation performed.

Write a program that would minimize the number of possible operations to transform any string x into a string y.

Input

The input consists of the strings x and y prefixed by their respective lengths, which are within 1000.

Output

An integer representing the minimum number of possible operations to transform any string x into a string y.

Sample Input

10 AGTCTGACGC
11 AGTAAGTAGGC

Sample Output

4
题意:
求由字符串s1,通过下列三种操作:
1.插入一个字符
2.删除一个字符
3.改变一个字符
变换的字符s2所需要 的最小操作次数。
思路:这是一个求编辑最短距离问题。利用动态规划,列出状态方程,设dp[i][j]表示字符串x[1...i]和字符串y[1...j]的最短编辑距离当x[i] == y[j]时,i和j不需要编辑,要么删除,要么插入,要么替换dp[i][j] = min(dp[i-1][j-1], dp[i-1][j] + 1, dp[i][j - 1] + 1)当x[i] != y[i]时, i和j不需要编辑dp[i][j] = min(dp[i-1][j-1] + 1, dp[i-1][j] + 1, dp[i][j-1] + 1);注意初始化dp[i][0] = dp[0][i] = i;
代码:
#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
const int maxn = 1010;
char strx[maxn], stry[maxn];
int lenx, leny, dp[maxn][maxn];
int main()
{

    while( scanf("%d %s", &lenx, strx  + 1) != EOF)
    {
        scanf("%d %s", &leny, stry + 1);
        int maxv = max(lenx, leny);
        dp[0][0] = 0;
        for(int i = 1; i <= maxv; i++)
            dp[0][i] = dp[i][0] = i;
        for(int i = 1; i <= lenx; i++)
        {
            for(int j = 1; j <= leny; j++)
            {
                dp[i][j] = min(dp[i-1][j] + 1, dp[i][j-1] + 1);
                if(strx[i] == stry[j])
                    dp[i][j] = min(dp[i][j], dp[i-1][j-1]);
                else
                    dp[i][j] = min(dp[i][j], dp[i-1][j-1] + 1);
            }
        }
        printf("%d\n", dp[lenx][leny]);
    }

    return 0;
}



版权声明:本文为博主原创文章,未经博主允许不得转载。

poj 3356

标签:

原文地址:http://blog.csdn.net/a1967919189/article/details/47705039

(0)
(0)
   
举报
评论 一句话评论(0
登录后才能评论!
© 2014 mamicode.com 版权所有  联系我们:gaon5@hotmail.com
迷上了代码!