40 lines
817 B
C++
40 lines
817 B
C++
// 107
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#include <bits/stdc++.h>
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using namespace std;
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int n;
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int a[500005], tmp[500005];
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long long ms(int l, int r)
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{
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if (l == r)
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return 0;
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int mid = l + r >> 1;
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long long ans = 0;
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ans = ms(l, mid) + ms(mid + 1, r);
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int i = l, j = mid + 1, tot = l;
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while (i <= mid && j <= r)
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{
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if (a[i] > a[j])
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tmp[tot++] = a[j++], ans+=j-tot;
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else
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tmp[tot++] = a[i++];
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}
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while (i <= mid)
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tmp[tot++] = a[i++];
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while (j <= r)
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tmp[tot++] = a[j++];
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for (int i = l; i <= r; ++i)
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a[i] = tmp[i];
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return ans;
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}
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int main()
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{
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scanf("%d", &n);
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while (n != 0)
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{
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for (int i = 1; i <= n; ++i)
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scanf("%d", &a[i]);
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printf("%lld\n", ms(1, n));
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scanf("%d", &n);
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}
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return 0;
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} |