Leetcode 1366:堆缓冲区溢出

Leetcode 1366: Heap Buffer Overflow

本文关键字：缓冲区 溢出 1366 Leetcode      更新时间：2023-10-16

这是我的 Leetcode 1366 代码，它不适用于某些测试用例，例如 ["XYZ"，"XZY"]

我对算法非常确定，即使用字符对和向量的向量作为映射。在我看来，代码有问题，而不是算法。

class Solution {
public:
string rankTeams(vector<string>& votes) {
int n = votes.size();
int m = votes[0].length();
if(n==1) return votes[0];
if(m==1) return votes[0];
string temp = votes[0];
sort(temp.begin(), temp.end());
vector<pair<char,vector<int>>> map(m);
vector<int> vec(m,0);
for(int i=0;i<m;i++){
map[i].first = temp[i];
map[i].second = vec;
}
//initialize the map
for(int i=0;i<n;i++){ //pick a voter
for(int j=0;j<m;j++){ //pick votes
map[votes[i][j] - 'A'].second[j]++;
}
}
sort(map.begin(), map.end(), [&](pair<char,vector<int>> pair1, pair<char,vector<int>> pair2){
for(int pos=0;pos<m;pos++){
if((pair1.second)[pos] > (pair2.second)[pos]) return true;
else if((pair1.second)[pos] < (pair2.second)[pos]) return false;
//else if((pair1.second)[pos] == (pair2.second)[pos]) continue;
}
return pair1.first < pair2.first;
});
string result;
for(int i=0;i<m;i++) result[i] =  map[i].first;
return result;
}
};

特别是，错误消息说 -

Runtime Error
=================================================================
==33==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x608000000308 at pc 0x00000038d06a bp 0x7ffe00621720 sp 0x7ffe00621718
READ of size 8 at 0x608000000308 thread T0
#4 0x7f57283cd82f  (/lib/x86_64-linux-gnu/libc.so.6+0x2082f)
Address 0x608000000308 is a wild pointer.
Shadow bytes around the buggy address:
0x0c107fff8010: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c107fff8020: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c107fff8030: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c107fff8040: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c107fff8050: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
=>0x0c107fff8060: fa[fa]fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c107fff8070: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c107fff8080: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c107fff8090: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c107fff80a0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c107fff80b0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
Shadow byte legend (one shadow byte represents 8 application bytes):
Addressable:           00
Partially addressable: 01 02 03 04 05 06 07 
Heap left redzone:       fa
Freed heap region:       fd
Stack left redzone:      f1
Stack mid redzone:       f2
Stack right redzone:     f3
Stack after return:      f5
Stack use after scope:   f8
Global redzone:          f9
Global init order:       f6
Poisoned by user:        f7
Container overflow:      fc
Array cookie:            ac
Intra object redzone:    bb
ASan internal:           fe
Left alloca redzone:     ca
Right alloca redzone:    cb
Shadow gap:              cc
==33==ABORTING

这个问题的"在线判断"中有一个错误，我想 LeetCode 应该会修复它。除此之外，以下解决方案是公认的解决方案，并且要简单得多：

class Solution {
public:
string rankTeams(vector<string> &votes) {
vector<vector<int>> count_map(26, vector<int>(27));
for (char &character : votes[0])
count_map[character - 65][26] = character;
for (string &vote : votes)
for (int index = 0; index < vote.length(); index++)
count_map[vote[index] - 65][index]--;
sort(count_map.begin(), count_map.end());
string sorted_teams;
for (int index = 0; index < votes[0].length(); index++)
sorted_teams += count_map[index][26];
return sorted_teams;
}
};

如果您要面试，请确保编写具有一致风格的干净代码。

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参考资料

  • 有关其他详细信息，您可以查看讨论区。其中有很多公认的解决方案、解释、多种语言的高效算法以及时间/空间复杂性分析。
  • ASCII 图表
  • 1366.按选票对团队进行排名
  • 1366. 按投票对团队进行排名 - 讨论区
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