I am trying to find a way to check if the elements of one list appears in another list in the same order in Java. For example:

char[] list = {'A','B','B','C','B','D'};
char[] sublist = {'B','C','B'};
char[] sublist2 = {'A','B','D'};

It should return true for sublist, but return false for sublist2 (because they do not appear in the same order). I am mainly trying to use for loops with some whiles and some ifs (trying not to use some built in functions maybe other than length).

I tried this but I do not think it is correct (getting wrong answers):

  public static boolean subList(char[] list, char[] sublist) {
      for(int i=0; i<sublist.length; i  ) {
          for(int j=0; j<list.length; j  ) {
               if (sublist[i] == list[j]) {
                   break;
               }
          }
          return true; 
       }
      return false;
  }

Is it possible to achieve this?

CodePudding user response：

This is not the most correct code but it works!

public static boolean subList(char[] list, char[] sublist) {
    int subposition=0;
    boolean subarray=false;
    for(int i=0;i<list.length;i  ) {
        if(subposition<sublist.length) {
            if(list[i]==sublist[subposition]) {
                subposition  ;
            }
            else if(subposition>0){
                subposition=0;
                i--;
            }
            if(subposition==sublist.length) {
                subarray=true;
            }
        }
    }
    if(subarray)return true;
    else return false;
}

CodePudding user response：

The following code should work:

• outer loop by list, nested loop by sublist
• create a boolean flag found
• in the nested loop compare elements of list starting from current position in the list, as soon as discrepancy is detected, found is reset to false
• if upon completing the nested loop, found is true then the sublist is detected.

public static boolean subList(char[] list, char[] sublist) {
    for(int i = 0; i < list.length; i  ) {
        boolean found = true;
        for(int j = 0, k = i; j < sublist.length && found && k < list.length; j  , k  ) {
            if (sublist[j] != list[k]) {
                found = false;
            }
        }
        if (found) return true;
    }
    return false;
}

Tests:

char[] list = {'A','B','B','C','B','D'};
char[] sublist = {'B','C','B'};
char[] sublist2 = {'A','B','D'};        
System.out.println(subList(list, sublist));  // true
System.out.println(subList(list, sublist2)); // false

CodePudding user response：

Try this.

public static boolean subList(char[] list, char[] sublist) {
    L: for (int i = 0, max = list.length - sublist.length; i <= max; i  ) {
        for (int j = 0, k = i; j < sublist.length; j  , k  )
            if (sublist[j] != list[k])
                continue L;
        return true;
    }
    return false;
}

public static void main(String[] args) throws InterruptedException {
    char[] list = {'A', 'B', 'B', 'C', 'B', 'D'};
    char[] sublist = {'B', 'C', 'B'};
    char[] sublist2 = {'A', 'B', 'D'};
    System.out.println(subList(list, sublist));
    System.out.println(subList(list, sublist2));
}

output:

true
false