LongestCommonSequence 最长连续公共子序列（算法导论是最长公共子序列）

import java.util.Scanner;
//最长连续公共子序列
//连续i子串的特点就是如果str1[i]和str2[j]是属于某公共子串的最后一个字符，
//那么一定有str1[i]==str2[j] && str1[i-1] == str2[j-1]，
//从矩阵中直观的看，就是由“1”构成的“斜线”代表的序列都是公共子串，
//那么最长公共子串肯定就是斜线“1”最长的那个串。

public class LongestCommonSequence {
/**
* @param args
*/
private int end1 = 0;
private int end2 = 0;

public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner scan = new Scanner(System.in);
String s1 = scan.next();
String s2 = scan.next();
LongestCommonSequence lcs = new LongestCommonSequence();
System.out.println(lcs.longestCommonSequence(s1, s2));
}

private String longestCommonSequence(String s1, String s2) {
if (s1 == null || s1.length() == 0 || s2 == null || s2.length() == 0) {
return null;
}
int[][] equals = new int[s1.length()][s2.length()];
for (int i = 0; i < s1.length(); i++) {
for (int j = 0; j < s2.length(); j++) {
if (s1.charAt(i) == s2.charAt(j)) {
equals[i][j] = 1;
} else {
equals[i][j] = 0;
}
}
}
int longestlen = getLongesPosition(equals, s1.length(), s2.length());
System.out.println(longestlen + " " + end1);
return s1.substring(end1 - longestlen + 1, end1 + 1);
}

private int getLongesPosition(int[][] equals, int len1, int len2) {
int max = 0;
for (int i = 0; i < len1; i++) {
int flag = i;
int len = 0;
for (int j = 0; j < (int) Math.min(len1, len2) && flag < len1; j++) {
if (equals[flag][j] == 1) {
len++;
} else {
if (len > max) {
max = len;
end1 = flag - 1;
end2 = j - 1;
}
len = 0;
}
flag++;
}
}
for (int i = 1; i < len2; i++) {
int flag = i;
int len = 0;
for (int j = 0; j < (int) Math.min(len1, len2) && flag < len2; j++) {
if (equals[j][flag] == 1) {
len++;
} else {
if (len > max) {
max = len;
end1 = j - 1;
end2 = flag - 1;
}
len = 0;
}
flag++;
}
}
return max;
}
}