POJ 2104 K-th Number 划分树

题意：

分析：

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

const int maxn = 100000 + 10;
const int maxd = 20;

int n, m;
int sorted[maxn];
int T[maxd][maxn], num[maxd][maxn];

void build(int d, int L, int R) {
int M = (L + R) / 2;
int lsame = M - L + 1;
for(int i = L; i <= R; i++) if(T[d][i] < sorted[M]) lsame--;
int lpos = L, rpos = M+1;
for(int i = L; i <= R; i++) {
if(i == L) num[d][i] = 0;
else num[d][i] = num[d][i - 1];
if(T[d][i] < sorted[M] || (T[d][i] == sorted[M] && lsame)) {
T[d+1][lpos++] = T[d][i];
num[d][i]++;
if(T[d][i] == sorted[M]) lsame--;
} else {
T[d+1][rpos++] = T[d][i];
}
}
if(L < M) build(d + 1, L, M);
if(M+1 < R) build(d + 1, M+1, R);
}

int query(int d, int L, int R, int qL, int qR, int k) {
if(L == R) return T[d][L];
int M = (L + R) / 2;
int cntl;
if(L == qL) cntl = 0;
else cntl = num[d][qL - 1];
int cntr = num[d][qR];
int cnt = cntr - cntl;
if(cnt >= k) return query(d + 1, L, M, L + cntl, L + cntr - 1, k);
else {
cntl = qL - L - cntl;
cntr = qR - L + 1 - cntr;
return query(d + 1, M+1, R, M+1+cntl, M+cntr, k - cnt);
}
}

int main()
{
scanf("%d%d", &n, &m);
for(int i = 1; i <= n; i++) {
scanf("%d", sorted + i);
T[0][i] = sorted[i];
}

sort(sorted + 1, sorted + 1 + n);
build(0, 1, n);

while(m--) {
int l, r, k; scanf("%d%d%d", &l, &r, &k);
printf("%d\n", query(0, 1, n, l, r, k));
}

return 0;
}