[20250407] BOJ / P3 / 수열과 쿼리 1 / 신희을

Author: ShinHeeEul

ShinHeeEul/202504/07 BOJ P3 수열과 쿼리1.md

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+```java
+
+import java.util.*;
+import java.io.*;
+
+class Main {
+
+	static Node[] segments;
+	static int N;
+	static int size = 1;
+	public static void main(String args[]) throws Exception {
+		N = read();
+		StringBuilder sb = new StringBuilder();
+		while(size < N) size <<= 1;
+		
+		segments = new Node[(size << 1) + 1];
+		
+		// 머지 소트 트리 구성하고
+		for(int i = size + 1 ; i < size + N + 1; i++) {
+			segments[i] = new Node();
+			segments[i].arr = new int[1];
+			segments[i].arr[0] = read();
+		}
+		
+		for(int i = size + N + 1 ; i < (size << 1) + 1; i++) {
+			segments[i] = new Node();
+			segments[i].arr = new int[1];
+			segments[i].arr[0] = 0;
+		}
+		int segmentSize = size << 1;
+		
+		
+		while(segmentSize > 2) {
+			merge(segments[segmentSize], segments[segmentSize - 1], 
+					segmentSize >> 1, segments[segmentSize].arr.length << 1);
+			segmentSize -= 2;
+		}
+		// 해당 범위 내에 포함될 때 이분 탐색으로 값 탐색하기
+		int M = read();
+		
+		while(M --> 0) {
+			sb.append(query(read(),read(),2,1, size, read())).append("\n");
+		}
+		
+		System.out.println(sb);
+	}
+	
+	public static void merge(Node left, Node right, int idx, int mergeSize) {
+		segments[idx] = new Node();
+		segments[idx].arr = new int[mergeSize];
+		
+		// 좌측 인덱스, 우측 인덱스
+		int leftIdx = 0;
+		int rightIdx = 0;
+		int end = (mergeSize >> 1);
+		// 더 작은 값을 업데이트 하고 다음 인덱스로 옮기기
+		for(int i = 0; i < mergeSize; i++) {
+			//System.out.println(leftIdx + " " + rightIdx);
+			if(rightIdx == end) {
+				segments[idx].arr[i] = left.arr[leftIdx];
+				leftIdx++;
+				continue;
+			} 
+			
+			if(leftIdx == end){
+				segments[idx].arr[i] = right.arr[rightIdx];
+				rightIdx++;
+				continue;
+			}
+      int a = left.arr[leftIdx];
+      int b = right.arr[rightIdx];
+			if(a < b) {
+				segments[idx].arr[i] = a;
+				leftIdx++;
+				continue;
+			} else {
+				segments[idx].arr[i] = b;
+				rightIdx++;
+				continue;
+			}
+		}
+	}
+	
+	public static int query(int left, int right, int node, int start, int end, int k) {
+		
+		if(end < left || right < start) return 0;
+		
+		if(left <= start && end <= right) {
+			// 이분 탐색
+			Node n = segments[node];
+			int l = 0;
+			int r = n.arr.length;
+			
+			while(l < r) {
+				int mid = (l + r) >> 1;
+				if(n.arr[mid] > k) {
+					r = mid;
+				} else {
+					l = mid + 1;
+				}
+			}
+			return n.arr.length - l;
+		}
+		
+		int mid = (start + end) >> 1;
+		return query(left, right, (node << 1) - 1, start, mid, k) + query(left, right, node << 1, mid + 1, end, k);
+		
+	}
+	
+	public static class Node {
+		int[] arr;
+	}
+
+    private static int read() throws Exception {
+        int d, o;
+        d = System.in.read();
+
+        o = d & 15;
+
+        while ((d = System.in.read()) > 32)
+            o = (o << 3) + (o << 1) + (d & 15);
+
+        return o;
+    }
+
+
+}
+```