本文實例講述了java實現求兩個字符串最大公共子串的方法。分享給大家供大家參考,具體如下:
最近在項目工作中有一個關於文本對比的需求,經過這段時間的學習,總結了這篇博客內容:求兩個字符串的最大公共子串。
算法思想:基於圖計算兩字符串的公共子串。具體算法思想參照下圖:
輸入字符串S1:achmacmh 輸入字符串S2:macham
具體的實現代碼如下所示:
package cn.lulei.compare; import java.util.ArrayList; import java.util.Collections; import java.util.Comparator; import java.util.List; public class StringCompare { private int a; private int b; public String getMaxLengthCommonString(String s1, String s2) { if (s1 == null || s2 == null) { return null; } a = s1.length();//s1長度做行b = s2.length();//s2長度做列if(a== 0 || b == 0) { return ""; } //設置匹配矩陣boolean [][] array = new boolean[a][b]; for (int i = 0; i < a; i++) { char c1 = s1.charAt(i); for (int j = 0; j < b; j++) { char c2 = s2.charAt(j); if (c1 == c2) { array[i][j] = true; } else { array[i][j] = false; } } } //求所有公因子字符串,保存信息為相對第二個字符串的起始位置和長度List<ChildString> childStrings = new ArrayList<ChildString>(); for (int i = 0; i < a; i++) { getMaxSort(i, 0, array, childStrings); } for (int i = 1; i < b; i++) { getMaxSort(0, i, array, childStrings); } //排序sort(childStrings); if (childStrings.size() < 1) { return ""; } //返回最大公因子字符串int max = childStrings.get(0).maxLength; StringBuffer sb = new StringBuffer(); for (ChildString s: childStrings) { if (max != s.maxLength) { break; } sb.append(s2.substring(s.maxStart, s.maxStart + s.maxLength)); sb.append("/n"); } return sb.toString(); } //排序,倒敘private void sort(List<ChildString> list) { Collections.sort(list, new Comparator<ChildString>(){ public int compare(ChildString o1, ChildString o2) { return o2.maxLength - o1.maxLength; } }); } //求一條斜線上的公因子字符串private void getMaxSort(int i, int j, boolean [][] array, List<ChildString> sortBean) { int length = 0; int start = j; for (; i < a && j < b; i++,j++) { if (array[i][j]) { length++; } else { sortBean.add(new ChildString(length, start)); length = 0; start = j + 1; } if (i == a-1 || j == b-1) { sortBean.add(new ChildString(length, start)); } } } //公因子類class ChildString { int maxLength; int maxStart; ChildString(int maxLength, int maxStart){ this.maxLength = maxLength; this.maxStart = maxStart; } } /** * @param args */ public static void main(String[] args) { // TODO Auto-generated method stub System.out.println(new StringCompare().getMaxLengthCommonString("achmacmh", "macham")); } }程序最終執行結果是:
對於兩個文件的比對個人認為可以參照這種算法思想(自己現在並為實現),在日後的博客中將會寫到。
上述實現過程中,用數組保存了所有的公共子串信息,然後排序取最大的子串,這種做法如果只是求最大子串的話,算法就不是很合理,因此做瞭如下修改,List只保存當前計算中最大的子串,具體實現如下:
/** *@Description: 字符串比較*/ package com.lulei.test; import java.util.ArrayList; import java.util.List; public class StringCompare { private int a; private int b; private int maxLength = -1; public String getMaxLengthCommonString(String s1, String s2) { if (s1 == null || s2 == null) { return null; } a = s1.length();//s1長度做行b = s2.length();//s2長度做列if(a== 0 || b == 0) { return ""; } //設置匹配矩陣boolean [][] array = new boolean[a][b]; for (int i = 0; i < a; i++) { char c1 = s1.charAt(i); for (int j = 0; j < b; j++) { char c2 = s2.charAt(j); if (c1 == c2) { array[i][j] = true; } else { array[i][j] = false; } } } //求所有公因子字符串,保存信息為相對第二個字符串的起始位置和長度List<ChildString> childStrings = new ArrayList<ChildString>(); for (int i = 0; i < a; i++) { getMaxSort(i, 0, array, childStrings); } for (int i = 1; i < b; i++) { getMaxSort(0, i, array, childStrings); } StringBuffer sb = new StringBuffer(); for (ChildString s: childStrings) { sb.append(s2.substring(s.maxStart, s.maxStart + s.maxLength)); sb.append("/n"); } return sb.toString(); } //求一條斜線上的公因子字符串private void getMaxSort(int i, int j, boolean [][] array, List<ChildString> sortBean) { int length = 0; int start = j; for (; i < a && j < b; i++,j++) { if (array[i][j]) { length++; } else { //直接add,保存所有子串,下面的判斷,只保存當前最大的子串//sortBean.add(new ChildString(length, start)); if (length == maxLength) { sortBean.add(new ChildString(length, start)); } else if (length > maxLength) { sortBean.clear(); maxLength = length; sortBean.add(new ChildString(length, start)); } length = 0; start = j + 1; } if (i == a-1 || j == b-1) { //直接add,保存所有子串,下面的判斷,只保存當前最大的子串//sortBean.add(new ChildString(length, start)); if (length == maxLength) { sortBean.add(new ChildString(length, start)); } else if (length > maxLength) { sortBean.clear(); maxLength = length; sortBean.add(new ChildString(length, start)); } } } } //公因子類class ChildString { int maxLength; int maxStart; ChildString(int maxLength, int maxStart){ this.maxLength = maxLength; this.maxStart = maxStart; } } /** * @param args */ public static void main(String[] args) { // TODO Auto-generated method stub System.out.println(new StringCompare().getMaxLengthCommonString("abcdef", "defabc")); } }感謝閱讀,希望能幫助到大家,謝謝大家對本站的支持!