为什么这个break语句不能按预期工作？

Question

I have this simple snippet of code with a break statement. I was trying to solve this http://codeforces.com/contest/787/problem/B . I came up with this solution:

public static void main(String[] args) {
    FastReader in = new FastReader();
    int n = in.nextInt(), m = in.nextInt();
    HashSet<Integer> set = new HashSet<>();
    for(int i=0;i<m;i++){
        set.clear();
        int k = in.nextInt();
        boolean cancel = true;
        for(int j=0;j<k;j++){
            int cur = in.nextInt();
            if(set.contains(-cur)){
                cancel = false;
                break;
            }
            else set.add(cur);
        }
        if(cancel && k!=0){
            System.out.println("YES");
            return;
        }
    }
    System.out.println("NO");
}

It didn't pass the tests, but the moment I remove the break statement after the cancel = false; line. It works. I can't seem to explain what the different between having the break statement so that when the first time you found -cur inside set you would change cancel to false then break and just assign false to cancel everytime you find -cur inside set and wait till the loop end and not break.

Answer 1

When you break out of for(int j=0;j<k;j++) , you don't read all the k numbers of that line of input (unless you were already at the last number).

For example, consider this input:

2 2
3 -1 1 -2
1 2

After having read -1 and 1, you program sets cancel to false and breaks out of the inner loop. Next time through the outer loop it will read -2 into k , and you've got it messed up.

When you remove the break statement, you are reading all the numbers correctly, and your program therefore works correctly.