京东后端开发笔试-5.14
笔试题分为两部分，选择题30题+编程题2题
编程题一：加密算法
字符串s打乱顺序后，前后加上任意字符串变为s‘，给定N组s和s'判断加密是否成功。
#include <iostream>
#include <string>
#include <vector>
using namespace std;
bool isValid(string s0, string s1) {
vector<int> hash(26,0);
for (int i = 0; i < s0.size(); i++) {
hash[s0[i] - 'a']++;
}
int left = 0;
int count = s0.size();
for (int i = 0; i < s1.size(); i++) {
hash[s1[i] - 'a']--;
while (left < s1.size() && hash[s1[i] - 'a'] < 0) {
hash[s1[left] - 'a']++;
left++;
}
if (i - left + 1 == count) return true;
}
return false;
}
int main() {
int N;
cin >> N;
for (int i = 0; i < N; i++) {
string s0, s1;
cin >> s0 >> s1;
if (isValid(s0, s1)) {
cout << "YES" << endl;
}
else {
cout << "NO" << endl;
}
}
return 0;
} 编程题二：树上拓扑 对于无根树进行拓扑排序。第一行输入N代表树的个数，下一行N-1个整数，[f2,f3,...fn] 代表i与fi之间有边。
//
// Created by Mozi on 2022/5/14.
//
#include <iostream>
#include <vector>
#include <queue>
using namespace std;
/*
* 题目：树上拓扑
* 样例输入：
* 6
* 1 2 1 3 3
*/
//创建树数组
vector<int> getTrees(int n) {
vector<int> trees(n - 1);
for (int i = 0; i < n - 1; i++) {
cin >> trees[i];
}
return trees;
}
vector<int> toposort(int n, vector<int>& trees) {
vector<int> ret;
vector<vector<int>> edges(n + 1); //边
vector<int> index(n + 1); //每个树相邻的树个数
for (int i = 0; i < trees.size(); i++) {
edges[i + 2].emplace_back(trees[i]);
edges[trees[i]].emplace_back(i + 2);
index[i + 2]++;
index[trees[i]]++;
}
//BFS广度优先
queue<int> q;
for (int i = 1; i <= n; i++) {
if (index[i] == 1) {
q.push(i);
}
}
while (!q.empty()) {
int cur = q.front();
q.pop();
ret.emplace_back(cur);
for (auto e : edges[cur]) {
index[e]--;
if (index[e] == 1) {
q.push(e);
}
}
}
return ret;
}
int main() {
int n;
cin >> n;
vector<int> trees = getTrees(n); //length:n-1
vector<int> ret = toposort(n, trees);
for (int i = 0; i < ret.size(); i++) {
if (i > 0) {
cout << " ";
}
cout << ret[i];
}
cout << endl;
return 0;
} 
