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# Find index of closing bracket for a given opening bracket in an expression

• Difficulty Level : Easy
• Last Updated : 22 Jul, 2022

Given a string with brackets. If the start index of the open bracket is given, find the index of the closing bracket.

Examples:

Input : string = [ABC[23]][89]
index = 0
Output : 8
The opening bracket at index 0 corresponds
to closing bracket at index 8.
Recommended Practice

The idea is to use Stack data structure. We traverse given expression from given index and keep pushing starting brackets. Whenever we encounter a closing bracket, we pop a starting bracket. If stack becomes empty at any moment, we return that index.

## C++

 // CPP program to find index of closing// bracket for given opening bracket.#include using namespace std;  // Function to find index of closing// bracket for given opening bracket.void test(string expression, int index){    int i;          // If index given is invalid and is     // not an opening bracket.    if(expression[index]!='['){        cout << expression << ", " <<                    index << ": -1\n";        return;    }          // Stack to store opening brackets.    stack st;          // Traverse through string starting from    // given index.    for(i = index; i < expression.length(); i++){                  // If current character is an         // opening bracket push it in stack.        if(expression[i] == '[')          st.push(expression[i]);                  // If current character is a closing        // bracket, pop from stack. If stack         // is empty, then this closing        // bracket is required bracket.        else if(expression[i] == ']'){            st.pop();            if(st.empty()){                cout << expression << ", " <<                        index << ": " << i << "\n";                return;            }        }    }          // If no matching closing bracket    // is found.    cout << expression << ", " <<                index << ": -1\n";}  // Driver Codeint main() {    test("[ABC[23]][89]", 0); // should be 8    test("[ABC[23]][89]", 4); // should be 7    test("[ABC[23]][89]", 9); // should be 12    test("[ABC[23]][89]", 1); // No matching bracket    return 0;}  // This code is contributed by Nikhil Jindal.

## Java

 // Java program to find index of closing // bracket for given opening bracket. import java.util.Stack;class GFG {  // Function to find index of closing // bracket for given opening bracket.     static void test(String expression, int index) {        int i;          // If index given is invalid and is         // not an opening bracket.         if (expression.charAt(index) != '[') {            System.out.print(expression + ", "                    + index + ": -1\n");            return;        }          // Stack to store opening brackets.         Stack st = new Stack<>();          // Traverse through string starting from         // given index.         for (i = index; i < expression.length(); i++) {              // If current character is an             // opening bracket push it in stack.             if (expression.charAt(i) == '[') {                st.push((int) expression.charAt(i));            } // If current character is a closing             // bracket, pop from stack. If stack             // is empty, then this closing             // bracket is required bracket.             else if (expression.charAt(i) == ']') {                st.pop();                if (st.empty()) {                    System.out.print(expression + ", "                            + index + ": " + i + "\n");                    return;                }            }        }          // If no matching closing bracket         // is found.         System.out.print(expression + ", "                + index + ": -1\n");    }  // Driver Code     public static void main(String[] args) {        test("[ABC[23]][89]", 0); // should be 8         test("[ABC[23]][89]", 4); // should be 7         test("[ABC[23]][89]", 9); // should be 12         test("[ABC[23]][89]", 1); // No matching bracket     }// this code is contributed by Rajput-Ji}

## Python

 # Python program to find index of closing# bracket for a given opening bracket.from collections import deque  def getIndex(s, i):      # If input is invalid.    if s[i] != '[':        return -1      # Create a deque to use it as a stack.    d = deque()      # Traverse through all elements    # starting from i.    for k in range(i, len(s)):          # Pop a starting bracket        # for every closing bracket        if s[k] == ']':            d.popleft()          # Push all starting brackets        elif s[k] == '[':            d.append(s[i])          # If deque becomes empty        if not d:            return k      return -1  # Driver code to test above method.def test(s, i):    matching_index = getIndex(s, i)    print(s + ", " + str(i) + ": " + str(matching_index))  def main():    test("[ABC[23]][89]", 0) # should be 8    test("[ABC[23]][89]", 4) # should be 7    test("[ABC[23]][89]", 9) # should be 12    test("[ABC[23]][89]", 1) # No matching bracket  if __name__ == "__main__":    main()

## C#

 // C# program to find index of closing // bracket for given opening bracket. using System;using System.Collections;public class GFG {   // Function to find index of closing // bracket for given opening bracket.     static void test(String expression, int index) {         int i;           // If index given is invalid and is         // not an opening bracket.         if (expression[index] != '[') {             Console.Write(expression + ", "                    + index + ": -1\n");             return;         }           // Stack to store opening brackets.         Stack st = new Stack();           // Traverse through string starting from         // given index.         for (i = index; i < expression.Length; i++) {               // If current character is an             // opening bracket push it in stack.             if (expression[i] == '[') {                 st.Push((int) expression[i]);             } // If current character is a closing             // bracket, pop from stack. If stack             // is empty, then this closing             // bracket is required bracket.             else if (expression[i] == ']') {                 st.Pop();                 if (st.Count==0) {                     Console.Write(expression + ", "                            + index + ": " + i + "\n");                     return;                 }             }         }           // If no matching closing bracket         // is found.         Console.Write(expression + ", "                + index + ": -1\n");     }   // Driver Code     public static void Main() {         test("[ABC[23]][89]", 0); // should be 8         test("[ABC[23]][89]", 4); // should be 7         test("[ABC[23]][89]", 9); // should be 12         test("[ABC[23]][89]", 1); // No matching bracket     } }   // This code is contributed by 29AjayKumar

Output:

[ABC[23]][89], 0: 8
[ABC[23]][89], 4: 7
[ABC[23]][89], 9: 12
[ABC[23]][89], 1: -1

Time Complexity: O(n)
Auxiliary Space: O(n)

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