Re: [閒聊] 每日LeetCode

[Rushia (みけねこ的鼻屎)]

https://leetcode.com/problems/sort-characters-by-frequency/description
451. Sort Characters By Frequency
給你一個字串s，把他的所有字元依照出現次數降序排列，如果答案有多個返回任意一個

思路：
1.先數s的每個字元有幾個
2.把s數量大於0的字元(計數索引)丟到MaxHeap依照數量排序
3.不斷從Heap取出字元並append成一個字串即可

Java Code：
--------------------------------------------
class Solution {
    public String frequencySort(String s) {
        int[] count = new int[252];
        for (char c : s.toCharArray()) {
            count[c]++;
        }
        PriorityQueue<Integer> heap = new PriorityQueue<>((a, b) -> count[b]
- count[a]);
        for (int i = 0; i < count.length; i++) {
            if (count[i] > 0) {
                heap.offer(i);
            }
        }

        StringBuilder sb = new StringBuilder();
        while (!heap.isEmpty()) {
            int idx = heap.poll();
            char ch = (char)(idx);
            for (int i = 0; i < count[idx]; i++) {
                sb.append(ch);
            }
        }
        return sb.toString();
    }
}
--------------------------------------------

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