HDU 2665 Kth number（划分树）

题目链接：点击打开链接

思路：划分树模板题。

细节参见代码：

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<iostream>
#include<string>
#include<vector>
#include<stack>
#include<bitset>
#include<cstdlib>
#include<cmath>
#include<set>
#include<list>
#include<deque>
#include<map>
#include<queue>
#define Max(a,b) ((a)>(b)?(a):(b))
#define Min(a,b) ((a)<(b)?(a):(b))
using namespace std;
typedef long long ll;
typedef long double ld;
const ld eps = 1e-9, PI = 3.1415926535897932384626433832795;
const int mod = 1000000000 + 7;
const int INF = 0x3f3f3f3f;
// & 0x7FFFFFFF
const int seed = 131;
const ll INF64 = ll(1e18);
const int maxn = 1e5 + 10;
int T,n,m;
int tree[20][maxn];
int sorted[maxn];
int toleft[20][maxn];
void build(int l, int r, int dep) {
if(l == r) return ;
int mid = (l + r) >> 1;
int same = mid - l + 1;
for(int i = l; i <= r; i++) {
if(tree[dep][i] < sorted[mid]) same--;
}
int lpos = l;
int rpos = mid + 1;
for(int i = l; i <= r; i++) {
if(tree[dep][i] < sorted[mid]) tree[dep+1][lpos++] = tree[dep][i];
else if(tree[dep][i] == sorted[mid] && same > 0) {
tree[dep+1][lpos++] = tree[dep][i];
same--;
}
else tree[dep+1][rpos++] = tree[dep][i];
toleft[dep][i] = toleft[dep][l-1] + lpos - l;
}
build(l, mid, dep+1);
build(mid+1, r, dep+1);
}
int query(int L, int R, int l, int r, int dep, int k) {
if(l == r) return tree[dep][l];
int mid = (L + R) >> 1;
int cnt = toleft[dep][r] - toleft[dep][l-1];
if(cnt >= k) {
int newl = L + toleft[dep][l-1] - toleft[dep][L-1];
int newr = newl + cnt - 1;
return query(L, mid, newl, newr, dep+1, k);
}
else {
int newr = r + toleft[dep][R] - toleft[dep][r];
int newl = newr - (r - l - cnt);
return query(mid+1, R, newl, newr, dep+1, k - cnt);
}
}
int l, r, k;
int main() {
scanf("%d",&T);
while(T--) {
memset(tree, 0, sizeof(tree));
scanf("%d%d",&n,&m);
for(int i = 1; i <= n; i++) {
scanf("%d",&tree[0][i]);
sorted[i] = tree[0][i];
}
sort(sorted+1, sorted+n+1);
build(1, n, 0);
while(m--) {
scanf("%d%d%d",&l, &r, &k);
printf("%d\n",query(1, n, l, r, 0, k));
}
}
return 0;
}