Interleaving String-1

// 没法考虑两个字符串的组合顺序问题。当处理{"aa", "ab", "aaba"}的时候，就不行了
// Merge sort
public class Interleaving_string {
 public static boolean isInterleave(String s1, String s2, String s3) {
        
        if (s3.length() != s2.length() + s1.length()) {
         return false;
        }
        int index = 0; //s3
        int n = 0;     //s1
        int m = 0;     //s2
        while(n < s1.length() && m < s2.length()) {
         if (s3.charAt(index) == s1.charAt(n)) {
          n++;
         } else if (s3.charAt(index) == s2.charAt(m)) {
          m++;
         } else {
          return false;
         }
         index++;
        }
        while (n < s1.length()) {
         if (s3.charAt(index) == s1.charAt(n)) {
          n++;
         } else {
          return false;
         }
         index++;
        }
        while (m < s2.length()) {
         if (s3.charAt(index) == s2.charAt(m)) {
          m++;
         } else {
          return false;
         }
         index++;
        }
 
        return true;

    }
 
}