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37 lines
1.0 KiB
C++
37 lines
1.0 KiB
C++
#include <algorithm>
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#include <cstdio>
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#include <cstring>
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using namespace std;
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int n, a[50001][2];
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int seq[50001], w[50001];
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int main()
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{
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scanf("%d", &n);
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for (int i = 1; i <= n; i++) scanf("%d%d", &a[i][0], &a[i][1]);
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int x = 0, ans1, ans2;
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for (int i = 1; i <= n; i++) x ^= a[i][0], x ^= a[i][1];
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if (x)
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printf("-1");
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else
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{
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seq[0] = 1, seq[1] = a[1][0];
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for (int i = 2; i < n; i++) seq[i] = a[seq[i - 1]][seq[i - 2] == a[seq[i - 1]][0]];
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if (seq[n - 1] != a[1][1])
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printf("-1");
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else
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{
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memset(w, 0, sizeof(w));
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for (int i = 0; i < n; i++)
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w[(seq[i] - i + n) % n]++;
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ans1 = *max_element(w, w + n);
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reverse(seq, seq + n);
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memset(w, 0, sizeof(w));
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for (int i = 0; i < n; i++)
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w[(seq[i] - i + n) % n]++;
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ans2 = *max_element(w, w + n);
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printf("%d", n - max(ans1, ans2));
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}
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}
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return 0;
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}
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