关于 C++ [重复] 中的排序()函数
原标题：Confused about the sort() function in C++ [duplicate]
This question already has answers here:
Why does flowing off the end of a non-void function without returning a value not produce a compiler error? (11 answers)
Closed 21 hours ago.
I ve just done a problem on Leetcode. But I was confused about the sort() function of C++.
This is more detail about it:
Given an array of integers nums, sort the array in increasing order based on the frequency of the values. If multiple values have the same frequency, sort them in decreasing order.
-Input: An array
-Output: Sorted array following the problem s rule
Here is my code.
First code snippet:
class Solution {
public:
vector frequencySort(vector& nums) {
std::map hm;
for (int numb : nums)
hm[numb] ++ ;
sort(nums.begin(), nums.end(), [&](int a,int b){
if(hm[a] == hm[b])
return a > b;
return hm[a] < hm[b];
});
}
}
The second code snippet:
class Solution {
public:
vector frequencySort(vector& nums) {
std::map hm;
for (int numb : nums)
hm[numb] ++ ;
vector arr;
for(auto &[numb,freq] : hm){
while(freq > 0){
arr.push_back(numb);
freq--;
}
}
std::sort(arr.begin(), arr.end(), [&](int a, int b){
if( hm[a] == hm[b])
return a > b;
else
return hm[a] < hm[b];
});
return arr;
}
};
Here s an example
-Input: [1,1,2,2,2,3]
-Output for first code snippet: [3,1,1,2,2,2]
-Output for second code snippet: [3,2,2,2,1,1]
The thing that I don t understand is why the second one s sort() function seems to not be working? Can anybody help me to make it clear, please?
I tried two code snippets with the same function but it seems to return two different results.
问题回答
Both functions are wrong.
The 1st function does not return anything, which is undefined behavior.
The 2nd function return s prematurely, skipping half of its code.
The compiler should have warned you about both mistakes. If it didn t, turn up the warning level.
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