51nod p1175 区间中第K大的数

1175 区间中第K大的数

基准时间限制：1 秒 空间限制：131072 KB 分值: 160 难度：6级算法题

 

一个长度为N的整数序列，编号0 - N - 1。进行Q次查询，查询编号i至j的所有数中，第K大的数是多少。

例如: 1 7 6 3 1。i = 1, j = 3，k = 2，对应的数为7 6 3，第2大的数为6。

 

Input

第1行：1个数N，表示序列的长度。(2 <= N <= 50000)
第2 - N + 1行：每行1个数，对应序列中的元素。(0 <= S[i] <= 10^9)
第N + 2行：1个数Q，表示查询的数量。(2 <= Q <= 50000)
第N + 3 - N + Q + 2行：每行3个数，对应查询的起始编号i和结束编号j，以及k。(0 <= i <= j <= N - 1,1 <= k <= j - i + 1)

Output

共Q行，对应每一个查询区间中第K大的数。

Input示例

5
1
7
6
3
1
3
0 1 1
1 3 2
3 4 2

Output示例

7
6
1

区间第k大，主席树写一发，使用java写的，顺便复习
吐槽---java真是慢，一定要离散化，c++随便写都过
而且没有sort，没有map，只有hashmap，真逊啊。。。。

 package p1175;

 import java.io.*;
 import java.util.*;

 import javax.management.Query;

 public class Main
 {
     public static class Node
     {
         int sum;
         Node lc, rc;
         public Node(Node t)
         {
             if(t == null)
             {
                 lc = rc = null;
                 sum = 0;
             }
             else
             {
                 lc = t.lc;
                 rc = t.rc;
                 sum = t.sum;
             }
         }
     }

     static final int N = 50010;

     public static void main(String[] args) throws IOException
     {
         // TODO Auto-generated method stub
         BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
         BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(System.out));
         int n = getInt(reader);
         int[] arr = new int[n], store = new int[n];
         for(int i = 0; i < n; i++) store[i] = arr[i] = getInt(reader);
         mergeSort(store, 0, n - 1);
         int len = 1;
         for(int i = 1; i < n; i++)
             if(store[i] != store[i - 1]) store[len++] = store[i];
         HashMap<Integer, Integer> myMap = new HashMap<Integer, Integer>();
         for(int i = 0; i < len; i++)
             myMap.put(store[i], i);
         for(int i = 0; i < n; i++)
             arr[i] = myMap.get(arr[i]);

         Node[] root = new Node[n + 1];
         Node last = null;
         for(int i = 0; i < n; i++)
         {
             root[i] = new Node(last);
             buildTree(root[i], arr[i], 0, len);
             last = root[i];
         }

         for(int m = getInt(reader); m > 0; m--)
         {
             int l = getInt(reader), r = getInt(reader), k = getInt(reader);
             int ans = queryKth(l > 0 ? root[l - 1] : null, root[r], k, 0, len);
             writer.write(store[ans] + "\r\n");
             writer.flush();
         }
     }

     public static int querySum(Node t)
     {
         if(t == null) return 0;
         return t.sum;
     }

     public static int queryKth(Node l, Node r, int kth, int left, int right)
     {
         if(left == right) return left;
         int mid = (left + right) >> 1, ret = -1;
         int lCnt = l == null ? 0 : querySum(l.rc), rCnt = r == null ? 0 : querySum(r.rc);
         if(rCnt - lCnt >= kth) ret = queryKth(l == null ? null : l.rc, r == null ? null : r.rc, kth, mid + 1, right);
         else ret = queryKth(l == null ? null : l.lc, r == null ? null : r.lc, kth - (rCnt - lCnt), left, mid);
         return ret;
     }

     public static void buildTree(Node x, int val, int left, int right)
     {
         if(left < right)
         {
             int mid = (left + right) >> 1;
             if(val <= mid)
             {
                 x.lc = new Node(x.lc);
                 buildTree(x.lc, val, left, mid);
             }
             else
             {
                 x.rc = new Node(x.rc);
                 buildTree(x.rc, val, mid + 1, right);
             }
         }
         x.sum++;
     }

     static int[] tmp = new int[N];
     public static void mergeSort(int[] arr, int l, int r)
     {
         if(l >= r) return;
         int mid = (l + r) >> 1;
         mergeSort(arr, l, mid);
         mergeSort(arr, mid + 1, r);
         int itL = l, itR = mid + 1, now = l;
         while(itL <= mid && itR <= r)
         {
             if(arr[itL] < arr[itR]) tmp[now++] = arr[itL++];
             else tmp[now++] = arr[itR++];
         }
         while(itL <= mid) tmp[now++] = arr[itL++];
         while(itR <= r) tmp[now++] = arr[itR++];
         for(int i = l; i <= r; i++) arr[i] = tmp[i];
     }

     public static int getInt(BufferedReader reader) throws IOException
     {
         char ch = ' ';
         for( ; !(ch >= '0' && ch <= '9'); ch = (char) reader.read()) ;
         int ret = 0;
         for( ; ch >= '0' && ch <= '9'; ch = (char) reader.read())
             ret = ret * 10 + ch - '0';
         return ret;
     }

 }