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43 lines
926 B
43 lines
926 B
/*求区间众数和
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第一行输入一个正整数n。第二行输入n个正整数，1<n<200000,1<=a<=2
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输入
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3
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2 1 2
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输出
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9
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*/
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#include <cstdio>
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#include <iostream>
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#include <algorithm>
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typedef long long LL;
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const int N = 200010;
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int n;
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int a[N], tr[N * 2];
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int sum[N];
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int lowbit(int x) {
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return x & -x;
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}
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void modify(int x, int k) {
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for (int i = x; i <= 2 * n + 5; i += lowbit(i)) tr[i] += k;
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}
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int query(int x) {
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int res = 0;
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for (int i = x; i; i -= lowbit(i)) res += tr[i];
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return res;
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}
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int main() {
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scanf("%d", &n);
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for (int i = 1; i <= n; i++) scanf("%d", &a[i]);
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LL ans = 0;
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modify(0 + n + 1, 1);
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for (int i = 1; i <= n; i++) {
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sum[i] = sum[i - 1];
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if (a[i] == 1) sum[i] += 1;
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else sum[i] -= 1;
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ans += query(sum[i] + n + 1) + (i - query(sum[i] + n + 1)) * 2;
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modify(sum[i] + n + 1, 1);
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}
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printf("%lld", ans);
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return 0;
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}
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