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HDU 2665 Kth number（劃分樹）

編輯：關於C

思路：劃分樹模板題。

細節參見代碼：

#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#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;
}