【代码随想录Day30】贪心算法Part04

452. 用最少数量的箭引爆气球

题目链接/文章讲解：代码随想录
视频讲解:贪心算法，判断重叠区间问题 | LeetCode：452.用最少数量的箭引爆气球_哔哩哔哩_bilibili

class Solution {
    public int findMinArrowShots(int[][] points) {
        Arrays.sort(points, new Comparator<int[]>() {
            public int compare(int[] o1, int[] o2) {
                return Integer.compare(o1[0], o2[0]);
            }
        });
        int count = 1;
        for (int i = 1; i < points.length; i++) {
            if (points[i][0] > points[i - 1][1]) {
                count++;
            } else {
                points[i][1] = Math.min(points[i][1], points[i - 1][1]);
            }
        }
        return count;
    }
}

435. 无重叠区间

题目链接/文章讲解：代码随想录
视频讲解:贪心算法，依然是判断重叠区间 | LeetCode：435.无重叠区间_哔哩哔哩_bilibili

class Solution {
    public int eraseOverlapIntervals(int[][] intervals) {
        Arrays.sort(intervals, new Comparator<int[]>() {
            public int compare(int[] o1, int[] o2) {
                return Integer.compare(o1[0], o2[0]);
            }
        });
        int count = 0;
        for (int i = 1; i < intervals.length; i++) {
            if (intervals[i][0] < intervals[i - 1][1]) {
                count++;
                intervals[i][1] = Math.min(intervals[i][1], intervals[i - 1][1]);
            }
        }
        return count;
    }
}

763.划分字母区间

题目链接/文章讲解：代码随想录
视频讲解:贪心算法，寻找最远的出现位置！ LeetCode：763.划分字母区间_哔哩哔哩_bilibili

class Solution {
    public List<Integer> partitionLabels(String s) {
        int[] last = new int[26];
        char[] charArray = s.toCharArray();

        // 记录每个字符最后出现的位置
        for (int i = 0; i < charArray.length; i++) {
            last[charArray[i] - 'a'] = i;
        }

        List<Integer> list = new ArrayList<>();
        int start = 0;
        int end = 0;

        for (int i = 0; i < charArray.length; i++) {
            // 更新当前分区的结束位置
            end = Math.max(end, last[charArray[i] - 'a']);

            // 如果当前位置是分区的结束位置，则记录分区长度并更新 start
            if (i == end) {
                list.add(end - start + 1);
                start = end + 1;
            }
        }

        return list;
    }
}