为什么此代码会出现分段错误？

Question

Alice is playing an arcade game and wants to climb to the top of the leaderboard and wants to track her ranking. Its leaderboard works like this:

-The player with the highest score is ranked number on the leaderboard.

-Players who have equal scores receive the same ranking number, and the next player(s) receive the immediately following ranking number.

For example, the four players on the leaderboard have high scores of 100, 90, 90 and 80. Those players will have ranks 1, 2, 2 and 3 respectively. If Alice's scores are 70, 80 and 105 her rankings after each game are 4th, 3rd and 1st.

#include <bits/stdc++.h>

using namespace std;


struct table{
    int rank;
    int score;
};

This is a modified binary search function iplementation for searching the score.

int search(vector<table> v,int low,int high,int n,int x){
    if(low<=high){
        int mid =(high+low)/2;
        if((v[mid].score==x) || (mid==0 && v[mid].score<x))
            return v[mid].rank;
        if(mid==n-1 && v[mid].score>x)
            return (v[mid].rank + 1);
        if(v[mid].score>x && x>v[mid+1].score && mid<n-1)
            return v[mid+1].rank;
        if(v[mid].score>x)
            return search(v,mid+1,high,n,x);
        else
            return search(v,low,mid-1,n,x);
    }
    return -1;
}

Main climbingLeaderboard function

vector<int> climbingLeaderboard(vector<int> scores, vector<int> alice) {
    vector<table> v;
    vector<int> res;
    int n = scores.size();
    int m = alice.size();
    int x=1;
    for(int i=0 ; i<n ; i++){
        if(scores[i]!=scores[i-1] && i>0)
            x++;

        v[i].rank = x;
        v[i].score = scores[i];
    }
    int z;
    for(int i=0 ; i<m ; i++){
        x=alice[i];
        z = search(v,0,n-1,n,x);
        res.push_back(z);
    }
    return res;
}

Driver Program

int main(){
    int scores_count;
    cin >> scores_count;
    vector<int> scores; `//vector for storing leaderboard scores`
    int k;
    for(int i=0 ; i<scores_count ; i++){
        cin >> k;
        scores.push_back(k);
    }
    int game_count;   `//number of games played by alice`
    vector<int> Alice;  `//vector for storing Alice's scores`
    for(int i=0 ; i<game_count ; i++){
        cin >> k;
        alice.push_back(k);
    }
    vector<int> result; `//vector for storing result rank of each game of Alice`
    result = climbingLeaderboard(scores,alice);
    for(auto i = result.begin() ; i!=result.end() ; i++){
        cout << *i << endl;
    }
    return 0;
}

Answer 1

问题：在您的 climbingLeaderboard 函数中，当 i 设置为 0 时，第一个循环将尝试访问 scores[i-1]，导致 [= 的负索引11=] 访问。

修复：将 for 循环更改为从 i=1 开始。

问题 2：您通过索引访问 v 而没有实例化任何结构来保存数据（例如 v[i].rank = x）。

修复 2：创建结构实例并将数据写入其中，然后将其推回向量 v。或者，将整个向量的内存保留为预分配。

问题 3：仔细检查，您的搜索功能肯定有问题。您可能应该将其与其余代码隔离开来进行测试。

Answer 2

核心Dump/Segmentation故障是由于访问不属于您的内存而导致的一种特定错误。 function:Main 攀登排行榜功能出错：

访问超出数组索引范围

从 I =1 开始循环，因为你正在做 score[i-1] ，在第一次迭代中这里会 score[-1] （索引）并且在 c++

中没有 -1 索引

for(int i=1; i<n ; i++){


    if(scores[i]!=scores[i-1] && i>0)
        x++;

    v[i].rank = x;
    v[i].score = scores[i];
}

为什么此代码会出现分段错误？

Why this code is giving segmentation fault?

binary-search

c++14