---
title: "L1-050 倒数第N个字符串"
created: 2025-11-28
tags:
  - 算法
---

# L1-050 倒数第N个字符串

## 题目 [L1-050 倒数第N个字符串](https://pintia.cn/problem-sets/994805046380707840/exam/problems/type/7?problemSetProblemId=994805080346181632&page=0)

![[image-c3f33c44.png]]

## 思路分析

将字符串作为26进制的数 与10进制相互转换

![[image-789f5b13.png]]

## 代码实现

```cpp
#include <bits/stdc++.h>
using namespace std;
#define endl '\n'
#define int long long
using ll = long long;
using ull = unsigned long long;
using PII = pair<int, int>;
using Pll = pair<ll, ll>;
int dx[4] = { -1,0,1,0 }, dy[4] = { 0,1,0,-1 };

const int inf = 0x3f3f3f3f;

ll qmi(ll a,ll k) {
	ll res=1;
	while(k) {
		if(k&1)	res=res*a;
		k>>=1;
		a=a*a;
	}
	return res;
}

signed main() {
	ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
	int l;
	cin>>l;
	int n;
	cin>>n;

	ll end=0;

//	for(int i=0;i<l;i++){
//		end+=25*pow(26,i);
//	}

	for (int i = 0; i < l; i++) {
		end += 25 * qmi(26, i);
	}

	ll idx=end-n+1;

	stack<char> ans;
	while(idx){
		ans.push('a'+(idx%26));
		idx/=26;
	}
    while(ans.size()<l){
        ans.push('a');
    }

	while(!ans.empty()) {
		cout<<ans.top();
		ans.pop();
	}

	return 0;
}
```

```cpp
#include <bits/stdc++.h>
using namespace std;
#define endl '\n'
#define int long long
using ll = long long;
using ull = unsigned long long;
using PII = pair<int, int>;
using Pll = pair<ll, ll>;
int dx[4] = { -1,0,1,0 }, dy[4] = { 0,1,0,-1 };

const int inf = 0x3f3f3f3f;

ll qmi(ll a,ll k) {
	ll res=1;
	while(k) {
		if(k&1)	res=res*a;
		k>>=1;
		a=a*a;
	}
	return res;
}

signed main() {
	ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
	int l;
	cin>>l;
	int n;
	cin>>n;

	ll end=0;

//	for(int i=0;i<l;i++){
//		end+=25*pow(26,i);
//	}

	for (int i = 0; i < l; i++) {
		end += 25 * qmi(26, i);
	}

	ll idx=end-n+1;

	stack<char> ans;
	for(int i = 0; i < l; ++i){
		ans.push('a'+(idx%26));
		idx/=26;
	}

	while(!ans.empty()) {
		cout<<ans.top();
		ans.pop();
	}

	return 0;
}
```

## 同类题型

## 视频讲解

---
⬅️ [[L1-049 天梯赛座位分配|L1-049 天梯赛座位分配]] 🏠 [[00-天梯赛]] ➡️ [[L1-051 打折|L1-051 打折]]