hdu 2689 Sort it(线段树)

#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;

const int maxn = 1005;

#define lson(x) ((x)<<1)
#define rson(x) (((x)<<1)|1)
int lc[maxn << 2], rc[maxn << 2], s[maxn << 2];

inline void pushup(int u) {
s[u] = s[lson(u)] + s[rson(u)];
}

void build (int u, int l, int r) {
lc[u] = l;
rc[u] = r;
s[u] = 0;

if (l == r)
return;

int mid = (l + r) >> 1;
build(lson(u), l, mid);
build(rson(u), mid + 1, r);
pushup(u);
}

void modify(int u, int x, int w) {
if (x == lc[u] && rc[u] == x) {
s[u] += w;
return;
}

int mid = (lc[u] + rc[u]) >> 1;
if (x <= mid)
modify(lson(u), x, w);
else
modify(rson(u), x, w);
pushup(u);
}

int query(int u, int l, int r) {
if (l <= lc[u] && rc[u] <= r)
return s[u];

int mid = (lc[u] + rc[u]) >> 1, ret = 0;
if (l <= mid)
ret += query(lson(u), l, r);
if (r > mid)
ret += query(rson(u), l, r);
return ret;
}

int N, arr[maxn];

int main () {
while (scanf("%d", &N) == 1) {
build (1, 0, 1000);
for (int i = 1; i <= N; i++)
scanf("%d", &arr[i]);

int ans = 0;
for (int i = N; i; i--) {
ans += query(1, 0, arr[i]);
modify(1, arr[i], 1);
}
printf("%d\n", ans);
}
return 0;
}