堆排序——LeetCode451. Sort Characters By Frequency

题目

Given a string, sort it in decreasing order based on the frequency of characters.

Example 1:

Input:
"tree"Output:
"eert"Explanation:
'e' appears twice while 'r' and 't' both appear once.
So 'e' must appear before both 'r' and 't'. Therefore "eetr" is also a valid answer.

Example 2:

Input:
"cccaaa"Output:
"cccaaa"Explanation:
Both 'c' and 'a' appear three times, so "aaaccc" is also a valid answer.
Note that "cacaca" is incorrect, as the same characters must be together.

Example 3:

Input:
"Aabb"Output:
"bbAa"Explanation:
"bbaA" is also a valid answer, but "Aabb" is incorrect.
Note that 'A' and 'a' are treated as two different characters

思路

这道题的意思是给一个字符串，要求对字符串里的字符顺序进行调整，使得调整后字符串里的字符是根据其出现频率从高到低排列。因此首先遍历这个字符串，利用map获得每个字符出现的频率，然后再使用堆排序，最后根据堆排序的结果重新构建新的字符串。

代码


typedef struct node{char ch;int fre;
};class Solution {public:vector<node>number;void maximun(int i, int heap_size) {int l, r, m;node temp;l = 2*i; r = 2*i+1; m = i;temp = number[i];if(l<=heap_size && number[l-1].fre>number[i-1].fre) {m = l;temp = number[l-1];}if(r<=heap_size && number[r-1].fre>number[m-1].fre) {m = r;temp = number[r-1];}if(m!=i) {number[m-1] = number[i-1];number[i-1] = temp;maximun(m, heap_size);}}void heap_build() {int i, j;for(i = number.size()/2; i>0; i--) {maximun(i, number.size());}}void heap_sort() {heap_build();int len, i, j;node temp;len = number.size();while(len>1) {temp = number[0];number[0] = number[len-1];number[len-1] = temp;maximun(1, len-1);len--;}}string frequencySort(string s) {int i, j;string res = "";map<char, int> m;map<char, int>::iterator iter;m.clear();for(i=0; i<s.length(); i++) {if(m.count(s[i])==0) {m[s[i]] = 1;}else {m[s[i]]++;}}number.clear();iter = m.begin();while(iter!=m.end()) {node t;t.ch = iter->first;t.fre = iter->second;number.push_back(t);iter++;}heap_sort();stringstream str;for(i=number.size()-1; i>=0; i--) {j = number[i].fre;while(j--) {res += number[i].ch;// res.append(number[i].ch.tostring());}}return res;}
};

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堆排序——LeetCode451. Sort Characters By Frequency

堆排序——LeetCode451. Sort Characters By Frequency

题目

思路

代码

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