Given a space-separated string str, the task is to find the first substring whose reverse is a word in the string. All the characters of the string are lowercase English alphabet. The string ends with #. If no such substring is present, return -1
Examples:
Input: str = “mango is sweet when nam en tastes it#”
Output: man
Explanation: Substring “man” is reversed to “nam” and it is a word in the given stringInput: str = “hello world#”
Output: -1
Approach:
- Store all the words of the string on a map.
- Find all the substrings of the string.
- For each substring, check whether the reverse of the substring is a word of the string. If no such substring exists, print -1.
Below is the implementation of the above approach.
C++
// C++ program to find first substring#include <bits/stdc++.h>using namespace std;// Function to find first substringstring first_substring(string s){ int n = s.length(), c = 0; string s1, s2; map<string, int> mpp; // Storing the words present in string for (int i = 0; i < n; i++) { if (s[i] == ' ' || s[i] == '#') { s1 = s.substr(c, i - c); mpp[s1] = 1; c = i + 1; } } // Calculating for all // possible valid substring. for (int i = 0; i < n; i++) { if (s[i] == ' ') { continue; } for (int j = 0; j < n; j++) { if (s[j] == ' ') { break; } s1 = s.substr(i, j - i + 1); s2 = s1; reverse(s1.begin(), s1.end()); if (mpp[s1]) { return s2; } } } return "-1";}// Driver codeint main(){ string s, s1; s = "mango is sweet when nam en tastes it#"; s1 = first_substring(s); cout << s1 << "\n"; return 0;} |
Java
// Java program to find first subStringimport java.util.*;class GFG{// Function to find first subStringstatic String first_subString(String s){ int n = s.length(), c = 0; String s1, s2; HashMap<String, Integer> mpp = new HashMap<String, Integer>(); // Storing the words present in String for (int i = 0; i < n; i++) { if (s.charAt(i) == ' ' || s.charAt(i) == '#') { s1 = s.substring(c, i); mpp.put(s1, 1); c = i + 1; } } // Calculating for all // possible valid subString. for (int i = 0; i < n; i++) { if (s.charAt(i) == ' ') { continue; } for (int j = 0; j < n; j++) { if (s.charAt(i) == ' ') { break; } s1 = s.substring(i, j - i + 1); s2 = s1; s1 = reverse(s1); if (mpp.containsKey(s1)) { return s2; } } } return "-1";}static String reverse(String input) { char[] a = input.toCharArray(); int l, r = a.length - 1; for (l = 0; l < r; l++, r--) { char temp = a[l]; a[l] = a[r]; a[r] = temp; } return String.valueOf(a);}// Driver codepublic static void main(String[] args){ String s, s1; s = "mango is sweet when nam en tastes it#"; s1 = first_subString(s); System.out.print(s1+ "\n");}}// This code is contributed by Rajput-Ji |
Python3
# Python3 program to find first substring # Function to find first substring def first_substring(s) : n = len(s); c = 0; mpp = {}; # Storing the words present in string for i in range(n) : if (s[i] == ' ' or s[i] == '#') : s1 = s[c: i]; mpp[s1] = 1; c = i + 1; # Calculating for all # possible valid substring. for i in range(n) : if (s[i] == ' ') : continue; for j in range(n) : if (s[j] == ' ') : break; s1 = s[i : j + 1]; s2 = s1; s1 = s1[::-1]; if s1 in mpp : if mpp[s1] : return s2; return "-1"; # Driver code if __name__ == "__main__" : s = "mango is sweet when nam en tastes it#"; s1 = first_substring(s); print(s1); # This code is contributed by AnkitRai01 |
C#
// C# program to find first subStringusing System;using System.Collections.Generic;class GFG{// Function to find first subStringstatic String first_subString(String s){ int n = s.Length, c = 0; String s1, s2; Dictionary<String, int> mpp = new Dictionary<String, int>(); // Storing the words present in String for (int i = 0; i < n; i++) { if (s[i] == ' ' || s[i] == '#') { s1 = s.Substring(c, i - c); mpp.Add(s1, 1); c = i + 1; } } // Calculating for all // possible valid subString. for (int i = 0; i < n; i++) { if (s[i] == ' ') { continue; } for (int j = 0; j < n; j++) { if (s[i] == ' ') { break; } s1 = s.Substring(i, j - i + 1); s2 = s1; s1 = reverse(s1); if (mpp.ContainsKey(s1)) { return s2; } } } return "-1";}static String reverse(String input) { char[] a = input.ToCharArray(); int l, r = a.Length - 1; for (l = 0; l < r; l++, r--) { char temp = a[l]; a[l] = a[r]; a[r] = temp; } return String.Join("", a);}// Driver codepublic static void Main(String[] args){ String s, s1; s = "mango is sweet when nam en tastes it#"; s1 = first_subString(s); Console.Write(s1 + "\n");}}// This code is contributed by Rajput-Ji |
Javascript
<script> // Javascript program to find first substring// Function to find first substringfunction first_substring(s){ var n = s.length, c = 0; var s1, s2; var mpp = new Map(); // Storing the words present in string for (var i = 0; i < n; i++) { if (s[i] == ' ' || s[i] == '#') { s1 = s.substring(c, i); mpp.set(s1, 1); c = i + 1; } } // Calculating for all // possible valid substring. for (var i = 0; i < n; i++) { if (s[i] == ' ') { continue; } for (var j = 0; j < n; j++) { if (s[j] == ' ') { break; } s1 = s.substring(i, j + 1); s2 = s1; s1 = s1.split('').reverse().join(''); if (mpp.has(s1)) { return s2; } } } return "-1";}// Driver codevar s, s1;s = "mango is sweet when nam en tastes it#";s1 = first_substring(s);document.write( s1 );</script> |
Output:
man
Time complexity: O(n2) where n is length of string
Auxiliary space: O(n) as it is using extra space for map mpp
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