字符交替（算法）

给出两个字符串，打印出所有由这两个字符串的字符交替组成的字符串，要求维持原有字符的相对顺序。

void printInterleavings(String s1,String s2){printInterleavings(s1,s2,"");}void printInterleavings(String s1, String s2, String soFar){if( (s1 == null || s1.length() == 0) && (s2 == null || s2.length() == 0))return ;if(s1 == null || s1.length() == 0){System.out.println(soFar + s2);return;} if(s2== null || s2.length() == 0){System.out.println(soFar + s1);return;}printfInterleavings(s1.substring(1), s2, soFar + s1.charAt(0));printfInterleavings(s1,s2.substring(1),  soFar + s2.charAt(0));}