检查是否区域内所有整数都被覆盖

You are given a 2D integer array ranges and two integers left and right. Each ranges[i] = [starti, endi] represents an inclusive interval between starti and endi.

Return true if each integer in the inclusive range [left, right] is covered by at least one interval in ranges. Return false otherwise.

An integer x is covered by an interval ranges[i] = [starti, endi] if starti <= x <= endi.

 

Example 1:

Input: ranges = [[1,2],[3,4],[5,6]], left = 2, right = 5
Output: true
Explanation: Every integer between 2 and 5 is covered:
- 2 is covered by the first range.
- 3 and 4 are covered by the second range.
- 5 is covered by the third range.

Example 2:

Input: ranges = [[1,10],[10,20]], left = 21, right = 21
Output: false
Explanation: 21 is not covered by any range.

 

Constraints:

• 1 <= ranges.length <= 50
• 1 <= starti <= endi <= 50
• 1 <= left <= right <= 50

/*
 * 思路：
 * 1. 使用流（Stream）来处理区间。
 * 2. 使用一个 HashSet 来存储所有被覆盖的整数。
 * 3. 遍历 left 到 right 的每个整数，检查它们是否都在 HashSet 中。
 */
import java.util.HashSet;
import java.util.Set;
import java.util.stream.IntStream;

public class Solution {
    public boolean isCovered(int[][] ranges, int left, int right) {
        Set<Integer> covered = new HashSet<>();
        for (int[] range : ranges) {
            IntStream.rangeClosed(range[0], range[1]).forEach(covered::add);
        }
        return IntStream.rangeClosed(left, right).allMatch(covered::contains);
    }
}

该题解采用了标记数组的方法来解决问题。首先，创建一个长度为51的数组tmp（考虑到题目中的整数范围可能从1到50），用于记录特定整数是否被覆盖。对于每个区间[starti, endi]，遍历该区间中的所有整数，并将对应的tmp数组中的值设为1，表示该整数已被覆盖。接着，遍历从left到right的所有整数，检查这些整数是否都在tmp数组中被标记为1（即被覆盖）。如果存在未被覆盖的整数，则直接返回False。如果所有整数都被覆盖，则返回True。

O(N+M)

O(1)