public int lcs(String str1, String str2) {
	
	if ( null == str1 || 0 == str1.length() || null == str2 || 0 == str2.length() )
		return 0;
	
	int[][] table = new int[ str1.length() + 1 ][str2.length() + 1];
	
	for (int i = 0; i <= str1.length(); i++) {
		
		for (int j = 0; j <= str2.length(); j++) {
			
			if ( 0 == i || 0 == j )
				table[i][j] = 0;
			
			else if (str1.charAt(i - 1) == str2.charAt(j - 1))
				table[i][j] = table[i - 1][j - 1] + 1;
			else
				table[i][j] = Math.max(table[i - 1][j], table[i][j - 1]);
		}
	}
	
	
	
	// 求出具体的最长公共子序列
	int index1 = str1.length();
	int index2 = str2.length();
	
	StringBuilder sb = new StringBuilder();
	
	while ( index1 > 0 && index2 > 0 ) {
		
		if ( str1.charAt(index1 - 1) == str2.charAt(index2 - 1) ) {
			index1--;
			index2--;
			sb.append( str1.charAt(index1) );
		}
		
		else if ( table[index1][index2] == table[index1 - 1][index2] ) 
			index1--;
		
		else
			index2--;
	}
	
	System.out.println( sb.reverse().toString() );
	
	
	
	return table[ str1.length() ][str2.length()];
	
}