CodingBat AP-1 scoresIncreasing练习题中return false与score=false的差异及问题原因问询

Let's start by breaking down what your original code does correctly, then dive into why changing that line breaks things.

First, the original code logic #

Your working solution checks each pair of consecutive scores:

• For every i, if scores[i+1] >= scores[i], it sets score = true (though this is actually redundant, we'll get to that later).
• If it finds any pair where scores[i+1] < scores[i], it uses return false; to immediately exit the method and return false to the caller.
• If the loop finishes without hitting that return, it means all pairs are valid, so it returns score (which will be true after the last valid pair).

The key difference between return false; and score=false; #

1. return false;:
   This does two critical things: it sets the method's return value to false, and it stops all execution of the method right away. As soon as you hit this line, the loop breaks, no more iterations run, and your method gives back false—which is exactly what you want, because you've already found evidence the array isn't increasing.

2. score=false;:
   This only updates the value of the score variable to false—it doesn't stop the loop or the method. The program will keep running the next iterations of the loop. Here's where the bug happens:

   • Suppose you have an array like [1, 3, 2, 4]. When i=1, scores[2] = 2 is less than scores[1] = 3, so score gets set to false.
   • But the loop doesn't stop! Next iteration, i=2, scores[3] =4 >= scores[2] =2, so score gets set back to true.
   • By the end of the loop, you return true—even though the array has a decreasing pair, which is totally wrong.

A quick side note on your original code #

You don't actually need the score variable at all! If the loop completes without hitting a return false;, that means every consecutive pair is valid. So you could simplify the method to:

public boolean scoresIncreasing(int[] scores) {
    for(int i = 0; i < scores.length-1; i++){
        if(scores[i+1] < scores[i]){
            return false;
        }
    }
    return true;
}

This works the same way, but it's cleaner and avoids any confusion with the score variable.

内容的提问来源于stack exchange，提问作者Mateusz