for i in range(len(s)-1, -1, -1):

这是一个Python的for循环语句，它的作用是从字符串s的最后一个字符开始，依次向前遍历每个字符，直到遍历到第一个字符为止。

具体来说，range(len(s)-1, -1, -1)表示一个逆序的索引序列，它从len(s)-1开始，每次减1，直到-1为止。因此，for循环中的i变量将依次取到s的最后一个字符的索引、倒数第二个字符的索引、倒数第三个字符的索引，以此类推，直到第一个字符的索引。

在循环体中，可以通过s[i]来获取当前遍历到的字符。因为是从后往前遍历，所以可以用这种方式来实现字符串的逆序输出、逆序遍历等操作。

相关问题

def longestPalindrome(s: str) -> str: n = len(s) if n < 2: return s dp = [[False for _ in range(n)] for _ in range(n)] max_len = 1 start = 0 for i in range(n): dp[i][i] = True for j in range(1, n): for i in range(j): if s[i] == s[j]: if j - i < 3: dp[i][j] = True else: dp[i][j] = dp[i+1][j-1] else: dp[i][j] = False if dp[i][j]: cur_len = j - i + 1 if cur_len > max_len: max_len = cur_len start = i return s[start:start+max_len] 翻译成c++

好的，以下是该 Python 代码的 C++ 版本：

#include <string>
#include <vector>
using namespace std;

class Solution {
public:
    string longestPalindrome(string s) {
        int n = s.size();
        if (n < 2) {
            return s;
        }
        vector<vector<bool>> dp(n, vector<bool>(n, false));
        int max_len = 1, start = 0;
        for (int i = 0; i < n; ++i) {
            dp[i][i] = true;
        }
        for (int j = 1; j < n; ++j) {
            for (int i = 0; i < j; ++i) {
                if (s[i] == s[j]) {
                    if (j - i < 3) {
                        dp[i][j] = true;
                    } else {
                        dp[i][j] = dp[i+1][j-1];
                    }
                } else {
                    dp[i][j] = false;
                }
                if (dp[i][j]) {
                    int cur_len = j - i + 1;
                    if (cur_len > max_len) {
                        max_len = cur_len;
                        start = i;
                    }
                }
            }
        }
        return s.substr(start, max_len);
    }
};

希望能够帮助到您！

import collections def solve_method(n: int) -> None: asc = True list_ = collections.deque() x = 1 for i in range(1, n + 1): arr = [0] * i if asc: for j in range(i): arr[j] = x x += 1 else: for j in range(i - 1, -1, -1): arr[j] = x x += 1 list_.appendleft(arr) asc = not asc res = [] head = "" for ints in list_: content = head for j in range(len(ints)): num = ints[j] content += str(num) content += "*" * (4 - len(str(num))) if j != len(ints) - 1: content += " " res.append(content) head += " " for s in reversed(res): print(s) if __name__ == "__main__": n = int(input()) solve_method(n) 改写以上代码，python

import collections

def solve_method(n):
asc = True
list_ = collections.deque()
x = 1
for i in range(1, n + 1):
arr = [0] * i
if asc:
for j in range(i):
arr[j] = x
x += 1
else:
for j in range(i - 1, -1, -1):
arr[j] = x
x += 1
list_.appendleft(arr)
asc = not asc

res = []
head = ""
for ints in list_:
content = head
for j in range(len(ints)):
num = ints[j]
content += str(num)
content += "*" * (4 - len(str(num)))
if j != len(ints) - 1:
content += " "
res.append(content)
head += " "

for s in reversed(res):
print(s)

if __name__ == "__main__":
n = int(input())
solve_method(n)