LCS,即最常公共子序列的的C语言解法。prepare_for_backdate(char，char，int，int)函数是为后面的回溯法求得最长公共子序列做准备，并可得到子序列长度。lcs(char，int，int)函数是输出子序列的。并用到了第一个函数的结果。因为要得到最终的子序列，要知道那些地方是可输出的位置，因此构造数组b[][]，当为1时表明当前位置匹配，可输出，为2时需要往上回溯，为3时需要往左回溯，直到找到下一个为1的位置。而c[][]数组是保存找子序列过程中匹配位数。-LCS, that is the most common public sequence of C language method. prepare_for_backdate (char, char, int, int) function is obtained by back behind the longest sequence to prepare the public and may be sub-sequence length. lcs (char, int, int) function is the output sub-sequences. And use the first results of a function. Because to obtain the final sequence, it is necessary to know where is the location of the output, so the array structure b [][], as 1:00 shows that match the current location can be output, 2:00 needs to back up for the 3:00 need to go back to the left until you find the next 1 position. And c [] [] array is to preserve the process of looking for sequence matching the median.