[20260204] BOJ / G4 / 암벽 등반 / 이인희

Author: LiiNi-coder

LiiNi-coder/202602/04 BOJ 암벽 등반.md

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+```java
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.awt.Point;
+import java.util.ArrayDeque;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Deque;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+public class Main {
+	private static int T = 0;
+	private static int N = 0;
+	/*
+
+	 */
+	private static List<Point> Points;
+	private static Map<Integer, int[]> DpPointsAtX;
+	private static boolean[] Visited;
+	public static void main(String[] args) throws IOException {
+		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+		Points = new ArrayList<Point>();
+		DpPointsAtX = new HashMap<>();
+
+		String[] tokens = br.readLine().split(" ");
+		// 0. bfs 큐에 시작지점 추가, 포인트 정렬
+		N = Integer.parseInt(tokens[0]);
+		T = Integer.parseInt(tokens[1]);
+		Visited = new boolean[N];
+		int n = N;
+		while(n-->0){
+			tokens = br.readLine().split(" ");
+			Points.add(new Point(Integer.parseInt(tokens[0]), Integer.parseInt(tokens[1])));
+		}
+		Points.sort((o1, o2) -> o1.x - o2.x);
+		Deque<long[]> q = new ArrayDeque<>( );
+		q.offer(new long[]{0, 0, 0});
+		long answer = 0;
+		while(!q.isEmpty()){
+		// 1. bfs시작
+			long[] qItem = q.poll();
+			long x = qItem[0]; long y = qItem[1]; long step = qItem[2];
+			if(y == T){
+				answer = step;
+				break;
+			}
+			int[] idxBoundOfPointsAtX = getPointsAtX((int) x);
+			for(int i = idxBoundOfPointsAtX[0]; i < idxBoundOfPointsAtX[1]; i++){
+				int ny = Points.get(i).y;
+				if(Math.abs(y - ny)>2){
+					continue;
+				}
+				if(Visited[i]) continue;
+				q.offer(new long[]{Points.get(i).x, ny, step+1});
+				Visited[i] = true;
+			}
+		}
+		// for(Map.Entry<Integer, int[]> entry : DpPointsAtX.entrySet()){
+		// 	System.out.println(entry.getKey() + " : " + Arrays.toString(entry.getValue()));
+		// }
+		System.out.println((answer != 0)? answer : -1);
+		// 2-0. dpPointsAtX에 있는지 확인
+		// 2. 현재 시작지점에서 x 차2인것들의 인덱스 범위 추론 -> pointsAtX
+		// 3. pointsAtX으로 pointsAtXY 를 구함(O(len(pointsAtX)))
+		// 4. dpPointsAtX 에 pointsAtXY를 저장
+
+		br.close();
+	}
+
+	private static int[] getPointsAtX(int x) {
+		int[] idxsPointsAtX = DpPointsAtX.get(x);
+		if(idxsPointsAtX == null){
+			//이분탐색으로 구해야함
+			int idxOfLowerBound = getLowerBound(x-2);
+			int idxOfUppderBound = getUppderBound(x+2);
+			//삽입
+			DpPointsAtX.putIfAbsent(x, new int[]{idxOfLowerBound, idxOfUppderBound});
+			idxsPointsAtX = DpPointsAtX.get(x);
+		}
+		return idxsPointsAtX;
+	}
+
+	private static int getUppderBound(int v) {
+		int l = -1; int r = Points.size();
+		while(l + 1 < r){
+			int mid = (l + r) / 2;
+			if(!(Points.get(mid).x > v)) {
+				l = mid;
+			}else{
+				r = mid;
+			}
+		}
+		return r;
+	}
+
+	private static int getLowerBound(int v) {
+		int l = -1; int r = Points.size();
+		while(l + 1 < r){
+			int mid = (l + r) / 2;
+			if(!(Points.get(mid).x >= v)) {
+				l = mid;
+			}else{
+				r = mid;
+			}
+		}
+		return r;
+	}
+
+}
+```