g0201_0300.s0218_the_skyline_problem.Solution Maven / Gradle / Ivy

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Java-based LeetCode algorithm problem solutions, regularly updated

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package g0201_0300.s0218_the_skyline_problem;

// #Hard #Top_Interview_Questions #Array #Heap_Priority_Queue #Ordered_Set #Divide_and_Conquer
// #Segment_Tree #Binary_Indexed_Tree #Line_Sweep

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.TreeMap;

public class Solution {
    public List> getSkyline(int[][] buildings) {
        List> list = new ArrayList<>();
        List lines = new ArrayList<>();
        for (int[] building : buildings) {
            lines.add(new int[] {building[0], building[2]});
            lines.add(new int[] {building[1], -building[2]});
        }
        lines.sort((a, b) -> a[0] == b[0] ? b[1] - a[1] : a[0] - b[0]);
        TreeMap map = new TreeMap<>();
        map.put(0, 1);
        int prev = 0;
        for (int[] line : lines) {
            if (line[1] > 0) {
                map.put(line[1], map.getOrDefault(line[1], 0) + 1);
            } else {
                int f = map.get(-line[1]);
                if (f == 1) {
                    map.remove(-line[1]);
                } else {
                    map.put(-line[1], f - 1);
                }
            }
            int curr = map.lastKey();
            if (curr != prev) {
                list.add(Arrays.asList(line[0], curr));
                prev = curr;
            }
        }
        return list;
    }
}