zoukankan      html  css  js  c++  java
  • LeetCode——Palindromic Substrings

    Question

    Given a string, your task is to count how many palindromic substrings in this string.

    The substrings with different start indexes or end indexes are counted as different substrings even they consist of same characters.

    Example 1:

    Input: "abc"

    Output: 3

    Explanation: Three palindromic strings: "a", "b", "c".

    Example 2:

    Input: "aaa"

    Output: 6

    Explanation: Six palindromic strings: "a", "a", "a", "aa", "aa", "aaa".

    Note:
    The input string length won't exceed 1000.

    Solution

    动态规划,依次求解长度为1,2,3...的子字符串是否为回文,用一个二维数组纪录,同时用一个计数器统计回文子字符串的个数。

    Code

    class Solution {
    public:
        int countSubstrings(string s) {
            if (s.length() == 0)
                return 0;
            int len = s.length();
            table.resize(len);
            for (int i = 0; i < len; i++)
                table[i].resize(len);
    
            int count = 0;
            for (int i = 0; i < len; i++) {
                table[i][i] = true;
                count++;
            }
            //  遍历长度为2,3...的子字符串是否为回文
            for (int i = 2; i <= len; i++) {
                for (int j = 0; j <= len - i; j++) {
                    int start = j;
                    int end = j + i - 1;
                    if (s[start] == s[end]) {
                        if (start + 1 < end - 1) {
                            if (table[start + 1][end - 1] == true) {
                                table[start][end] = true;
                                count++;
                            } else {
                                table[start][end] = false;
                            }
                        } else {
                            table[start][end] = true;
                            count++;
                        }
                    } else {
                        table[start][end] = false;
                    }
                }
            }
            
            return count;
        }
        vector<vector<bool> >  table;
    };
    
  • 相关阅读:
    闭包
    this
    函数声明,表达式,构造函数
    算法学习_栈
    LeetCode刷题_140
    2020/3/20 刷题
    2020/3/19 刷题
    2020/3/13_C++实验课
    刷题(主要是DFS) 2020年3月12日
    DFS的一些题2020/3/11
  • 原文地址:https://www.cnblogs.com/zhonghuasong/p/7500863.html
Copyright © 2011-2022 走看看