算法训练Day35|860.柠檬水找零 ● 406.根据身高重建队列 ● 452. 用最少数量的箭引爆气球

 1class Solution {
 2    public boolean lemonadeChange(int[] bills) {
 3        // 映射
 4        Map<Integer, Integer> map = new HashMap<>(); 
 5        map.put(5, 0);
 6        map.put(10, 0);
 7        for (int i = 0; i < bills.length; i++) {
 8            if (bills[i] == 5) {
 9                map.put(5, map.get(5) + 1);
10            } else if (bills[i] == 10) {
11                if (map.get(5) > 0) {
12                    map.put(5, map.get(5) - 1);
13                    map.put(10, map.get(10) + 1);
14                } else {
15                    return false;
16                }
17            } else if (bills[i] == 20){
18                if (map.get(5) > 0 && map.get(10) > 0) {
19                    map.put(5, map.get(5) - 1);
20                    map.put(10, map.get(10) - 1);
21                } else if (map.get(5) >= 3){
22                    map.put(5, map.get(5) - 3);
23                } else {
24                    return false;
25                }
26            }
27        }
28        return true;
29    }
30}

 1class Solution {
 2    public int[][] reconstructQueue(int[][] people) {
 3        Arrays.sort(people, (a, b) -> a[0] == b[0] ? a[1] - b[1] : b[0] - a[0]);
 4
 5        List<int[]> list = new ArrayList<>();
 6
 7        for (int i = 0; i < people.length; i++) {
 8            int[] person = people[i];
 9            list.add(person[1], person);
10        }
11        return list.toArray(new int[people.length][]);
12    }
13}

 1class Solution {
 2    public int findMinArrowShots(int[][] points) {
 3        Arrays.sort(points, (a, b) -> Integer.compare(a[0] , b[0]));
 4
 5        int count = 1;
 6        for (int i = 1; i < points.length; i++) {
 7            if (points[i][0] > points[i - 1][1]) {
 8                count++;
 9            } else {
10                points[i][1] = Math.min(points[i - 1][1], points[i][1]);
11            }
12        }
13        return count;
14    }
15}