Pairs involved in Balanced Parentheses
Given a string of brackets, task is to find the number of pairs of brackets involved in a balanced sequence in a given range.
Examples :
Input : ((())(()
Range : 1 5
Range : 3 8
Output : 2
2
Explanation : In range 1 to 5 ((()),
there are the two pairs. In range 3 to 8 ())
((), there are the two pairs.
Input : )()()))
Range : 1 2
Range : 4 7
Output : 0
1
Explanation : In range 1 to 2 )( there
is no any pair. In range 4 to 7 ())),
there is the only pair
Prerequisite : Segment Trees
Approach :
Here, in segment tree, for each node, keep some simple elements, like integers or sets or vectors or etc.
For each node keep three integers :
1. t = Answer for the interval.
2. o = The number of opening brackets ‘(‘ remaining after deleting the brackets those who belong to the correct bracket sequence in this interval whit length t.
3. c = The number of closing brackets ‘)’ remaining after deleting the brackets those who belong to the correct bracket sequence in this interval whit length t.
Now, having these variables, queries can be answered easily using segment tree.
Below is the implementation of above approach :
C++
// CPP code to find the number of pairs // involved in balanced parantheses #include <bits/stdc++.h> using namespace std; // Our struct node struct node { // three variables required int t, o, c; }; // Declare array of nodes of very big // size which acts as segment tree here. struct node tree_arr[5 * 1000]; // To bulid a segment tree we pass 1 as // 'id' 0 as 'l' and l as 'n'. // Here, we consider query's interval as [x, y) void build(int id, int l, int r, string s) { /* this base condition is common to build any segment tree*/ // This is the base // Only one element left if (r - l < 2) { // If that element is open bracket if (s[l] == '(') tree_arr[id].o = 1; // If that element is open bracket else tree_arr[id].c = 1; return; } // Next three lines are common // for any segment tree. int mid = (l + r) / 2; // for left tree build(2 * id, l, mid, s); // for right tree build(2 * id + 1, mid, r, s); // Here we take minimum of left tree // opening brackets and right tree // closing brackets int tmp = min(tree_arr[2 * id].o, tree_arr[2 * id + 1].c); // we add that to our answer. tree_arr[id].t = tree_arr[2 * id].t + tree_arr[2 * id + 1].t + tmp; // Remove the answer from opening brackets tree_arr[id].o = tree_arr[2 * id].o + tree_arr[2 * id + 1].o - tmp; // Remove the answer from opening brackets tree_arr[id].c = tree_arr[2 * id].c + tree_arr[2 * id + 1].c - tmp; } // This will return the answer for each query. // Here we consider query's interval as [x, y) node segment(int x, int y, int id, int l, int r, string s) { // If the given interval is out of range if (l >= y || x >= r) { struct node tem; tem.t = 0; tem.o = 0; tem.c = 0; return tem; } // If the given interval completely lies if (x <= l && r <= y) return tree_arr[id]; // Next three lines are common for // any segment tree. int mid = (l + r) / 2; // For left tree struct node a = segment(x, y, 2 * id, l, mid, s); // For right tree struct node b = segment(x, y, 2 * id + 1, mid, r, s); // Same as made in build function int temp; temp = min(a.o, b.c); struct node vis; vis.t = a.t + b.t + temp; vis.o = a.o + b.o - temp; vis.c = a.c + b.c - temp; return vis; } // Driver code int main() { string s = "((())(()"; int n = s.size(); // range for query int a = 3, b = 8; build(1, 0, n, s); // Here we consider query's interval as [a, b) // We subtract 1 from 'a' because indexes start // from 0. struct node p = segment(a-1, b, 1, 0, n, s); cout << p.t << endl; return 0; } |
Python3
# Python3 code to find the number of pairs # involved in balanced parantheses # Our struct node class node : def __init__(self): # three variables required self.t = 0 self.o = 0 self.c = 0 # Declare array of nodes of very big # size which acts as segment tree here. tree_arr = [node()]*(5 * 1000) # To bulid a segment tree we pass 1 as # 'id' 0 as 'l' and l as 'n'. # Here, we consider query's interval as [x, y) def build(id, l, r, s): global tree_arr tree_arr[id] = node() # this base condition is common to # build any segment tree # This is the base # Only one element left if (r - l < 2) : # If that element is open bracket if (s[l] == "("): tree_arr[id].o = 1 # If that element is open bracket else: tree_arr[id].c = 1 return # Next three lines are common # for any segment tree. mid = int( (l + r) / 2) # for left tree build(2 * id, l, mid, s) # for right tree build(2 * id + 1, mid, r, s) # Here we take minimum of left tree # opening brackets and right tree # closing brackets tmp = min(tree_arr[2 * id].o, tree_arr[2 * id + 1].c) # we add that to our answer. tree_arr[id].t = tree_arr[2 * id].t + \ tree_arr[2 * id + 1].t + tmp # Remove the answer from opening brackets tree_arr[id].o = tree_arr[2 * id].o + \ tree_arr[2 * id + 1].o - tmp # Remove the answer from opening brackets tree_arr[id].c = tree_arr[2 * id].c + \ tree_arr[2 * id + 1].c - tmp # This will return the answer for each query. # Here we consider query's interval as [x, y) def segment(x, y, id, l, r, s): global tree_arr # If the given interval is out of range if (l >= y or x >= r) : tem= node() tem.t = 0 tem.o = 0 tem.c = 0 return tem # If the given interval completely lies if (x <= l and r <= y): return tree_arr[id] # Next three lines are common for # any segment tree. mid = int((l + r) / 2) # For left tree a = segment(x, y, 2 * id, l, mid, s) # For right tree b = segment(x, y, 2 * id + 1, mid, r, s) # Same as made in build function temp= 0 temp = min(a.o, b.c) vis = node() vis.t = a.t + b.t + temp vis.o = a.o + b.o - temp vis.c = a.c + b.c - temp return vis # Driver code s = "((())(()"n = len(s) # range for query a = 3b = 8 build(1, 0, n, s) # Here we consider query's interval as [a, b) # We subtract 1 from 'a' because indexes start # from 0. p = segment(a-1, b, 1, 0, n, s) print(p.t ) # This code is contributed by Arnab Kundu |
Output:
2
