As promised, here are some (nested) hints for Codeforces Round #682 (Div. 2).
1438A - Специфичные вкусы Андре
Hint 1
Hint 1
Hint 1
Hint 1
I wasn't able to solve E and F. If you did, you may want to add your hints in the comments.
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Unofficial hints for Codeforces Round #682 (Div. 2) (A — D)
As promised, here are some (nested) hints for Codeforces Round #682 (Div. 2).
1438A - Специфичные вкусы Андре
Solve some small tests on paper.
Can you make the sum of each subarray equal to its length?
Suppose that the answer is NO. Which property should hold for the array $$$a$$$?
What happens if $$$l_1 = r_1$$$?
The answer is YES if there is a pair of equal elements in the array $$$b$$$. What happens if there are no equal elements?
Look at the binary representation of the sum of each subarray. Are there equal binary representations?
Solve on paper
3 3
1 1 1
1 1 1
1 1 1
Now solve
3 3
2 1 1
1 1 2
2 1 2
Do a chess coloring on the grid. Can you make all differences odd?
How does the xor of all the array change after every operation?
The xor remains constant. Let it be $$$x$$$. If you make all elements equal, what's the xor of the resulting array?
If $$$n$$$ is even, $$$x = 0$$$. So the answer is NO if the starting xor is not $$$0$$$.
If $$$n$$$ is odd, you can set $$$a[i] = x$$$ for each $$$i$$$, and their xor is $$$x$$$. The answer is always YES.
In both cases, if the answer is YES, you can solve the problem by making each $$$a[i]$$$ equal to $$$x$$$. Can you make $$$a[1] = x$$$ first?
Now you want to "spread" $$$x$$$ in all the array. You already have some $$$a[i] = x$$$. Are there three indices such that $$$a[i] \oplus a[j] \oplus a[k] = x$$$?
I wasn't able to solve E and F. If you did, you may want to add your hints in the comments.
| Rev. | Lang. | By | When | Δ | Comment | |
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| en6 |
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TheScrasse | 2020-11-13 20:59:08 | 17 | Tiny change: '\nThe xor remains c' -> '\nThe xor of all the array remains c' | |
| en5 |
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TheScrasse | 2020-11-13 20:46:19 | 97 | ||
| en4 |
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TheScrasse | 2020-11-13 20:32:22 | 34 | Tiny change: 'he array. Are ther' -> 'he array. You already have some $a[i] = x$. Are ther' | |
| en3 |
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TheScrasse | 2020-11-13 20:25:47 | 24 | Tiny change: 'th cases, you can ' -> 'th cases, if the answer is `YES`, you can ' | |
| en2 |
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TheScrasse | 2020-11-13 20:21:01 | 76 | ||
| en1 |
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TheScrasse | 2020-11-13 20:18:34 | 2080 | Initial revision (published) |
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