【HDOJ】2492 Ping pong
线段树+离散化。
1 #include <cstdio> 2 #include <cstring> 3 #include <cstdlib> 4 5 #define MAXN 20005 6 #define lson l, mid, rt<<1 7 #define rson mid+1, r, rt<<1|1 8 9 int buf[MAXN], bk[MAXN]; 10 int sum[MAXN<<2], n; 11 12 int comp(const void *a, const void *b) { 13 return *(int *)a - *(int *)b; 14 } 15 16 void PushUP(int rt) { 17 sum[rt] = sum[rt<<1] + sum[rt<<1|1]; 18 } 19 20 void build(int l, int r, int rt) { 21 sum[rt] = 0; 22 if (l == r) 23 return ; 24 int mid = (l+r)>>1; 25 build(lson); 26 build(rson); 27 } 28 29 int query(int ll, int rr , int l, int r, int rt) { 30 if (ll<=l && r<=rr) 31 return sum[rt]; 32 int mid = (l+r)>>1; 33 int ret = 0; 34 if (ll <= mid) 35 ret += query(ll, rr, lson); 36 if (rr > mid) 37 ret += query(ll, rr, rson); 38 return ret; 39 } 40 41 void update(int x, int l, int r, int rt) { 42 if (l == r) { 43 ++sum[rt]; 44 return ; 45 } 46 int mid = (l+r)>>1; 47 if (x <= mid) 48 update(x, lson); 49 else 50 update(x, rson); 51 PushUP(rt); 52 } 53 54 int getIndex(int x) { 55 int l=1, r=n, mid; 56 57 while (l <= r) { 58 mid = (l+r)>>1; 59 if (bk[mid] == x) 60 return mid; 61 if (x > bk[mid]) 62 l = mid + 1; 63 else 64 r = mid - 1; 65 } 66 return 0; 67 } 68 69 int main() { 70 int t; 71 int i; 72 int index; 73 __int64 ll, lg, rl, rg; 74 __int64 ans; 75 76 scanf("%d", &t); 77 while (t--) { 78 scanf("%d", &n); 79 for (i=1; i<=n; ++i) { 80 scanf("%d", &buf[i]); 81 bk[i] = buf[i]; 82 } 83 build(1, n, 1); 84 qsort(bk+1, n, sizeof(int), comp); 85 ans = 0; 86 for (i=1; i<=n; ++i) { 87 index = getIndex(buf[i]); 88 ll = query(1, index, 1, n, 1); 89 lg = i-1-ll; 90 rl = index-1-ll; 91 rg = n-index-lg; 92 ans += ll*rg + lg*rl; 93 update(index, 1, n ,1); 94 } 95 printf("%I64d\n", ans); 96 } 97 98 return 0; 99 }
