g0601_0700.s0699_falling_squares.Solution Maven / Gradle / Ivy

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Java-based LeetCode algorithm problem solutions, regularly updated

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package g0601_0700.s0699_falling_squares;

// #Hard #Array #Ordered_Set #Segment_Tree #2022_03_22_Time_8_ms_(91.03%)_Space_42.8_MB_(90.38%)

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Set;
import java.util.TreeSet;

public class Solution {
    public List fallingSquares(int[][] positions) {
        // Coordinate compression using TreeSet
        Set unique = new TreeSet<>();
        for (int[] square : positions) {
            unique.add(square[0]);
            unique.add(square[0] + square[1] - 1);
        }
        // converted the TreeSet to a List
        List sorted = new ArrayList<>(unique);
        // Storing the max heights for compressed coordinates
        int[] heights = new int[sorted.size()];
        // Our answer list
        List list = new ArrayList<>(positions.length);
        // Global Max
        int max = 0;
        for (int[] square : positions) {
            // coordinate compression lookup
            int x1 = Collections.binarySearch(sorted, square[0]);
            int x2 = Collections.binarySearch(sorted, square[0] + square[1] - 1);
            // get the current max for the interval between x1 and x2
            int current = 0;
            for (int i = x1; i <= x2; i++) {
                current = Math.max(current, heights[i]);
            }
            // add the new square on the top
            current += square[1];
            // update the interval with the new value
            for (int i = x1; i <= x2; i++) {
                heights[i] = current;
            }
            // recalculate the global max
            max = Math.max(max, current);
            list.add(max);
        }
        return list;
    }
}