确保所有输入都是唯一数字的最佳方法是什么

Question

Here is an example inputs:

String test = "1 2 3 4 5 42"; String test2 = test.replaceAll(" ","");

public static boolean uniqueNumbers(String test2) {
    char[] testEntries= test2.toCharArray();
    Set<Character> set = new HashSet<>();
    
    for (int i = 0 ; i < testEntries.length ; i++ ) {
        if(!set.add(testEntries[i])) {
            return false;
        }
    }
    return true;
}

Despite all are unique number, it will return as false. Is there a way to fix this?

Answer 1

You should split your input argument with split() at first.

String test = "1 2 3 4 5 42";
String[] origin = test.split(" ");
Set<String> check = new HashSet<>(Arrays.asList(origin));
for (String el : check) {
    System.out.println(el);
}

Answer 2

Catch IllegalArgumentException from Set.of

The Set.of convenience method in Java 9+ creates a Set of an unspecified implementation when passed an array. If any duplicates are encountered while building this Set , an exception is thrown. You can trap for that IllegalArgumentException to know if the parts of your string are distinct or not.

We can get an array of the parts of your string by calling String#split .

Boolean isDistinct;
try
{
    Set.of( "1 3 3 4 5 42".split( " " ) );
    isDistinct = Boolean.TRUE;
}
catch ( IllegalArgumentException e )
{
    isDistinct = Boolean.FALSE;
}

System.out.println( "Input is distinct: " + Objects.requireNonNull( isDistinct ) );

See this code run live at Ideone.com .

Input is distinct: false

Answer 3

By the time you are passing your String parameter to uniqueNumbers() it looks like

1234542

Splitting it into char array takes each single character as a separate element, printing out the output immediately for instance gives:

char[] testEntries = test2.toCharArray();
System.out.println(Arrays.toString(testEntries));
//output: [1, 2, 3, 4, 5, 4, 2]

So when passing each element to the set, it finds 2 repeated at index 1 and 6.

One solution in this case would be to pass the original to split test using String's instance split().

    String test = "1 2 3 4 5 42";
    String[] test2=test.split(" ");


    public static boolean uniqueNumbers(String testEntries[]) {

    Set<String> set = new HashSet<>();

    for (int i = 0; i < testEntries.length; i++) {
        if (!set.add(testEntries[i])) {
            return false;
        }
    }
    return true;
}

//output: true