Advanced Recursion Problems | C++ Placement

Recursion - II

 

Permutation 

To print all the permutations of a string. 

Idea: for each character s[i] in the given string, we add a character in the ans string and then solve solve s.substr(0,i) + s.substr(i+1) 

 

Sample Input:  

ABC 

Sample Output: 

ABC 

ACB 

BAC 

BCA 

CAB 

CBA 

 

Time Complexity: O(N*2n )  

Space Complexity: O(2n ) 

 


  permutation(s, “”) will give the required answer 

 CountPaths 

Find the number of ways to reach e from s.  Idea: 

We have 6 ways to go forward (1,2,3,4,5,6). 

At the starting point s,  

Current answer = countPath(s+1,e) + countPath(s+2,e) + countPath(s+3,e) + countPath(s+4,e) + countPath(s+5,e) + countPath(s+6,e) 

Time Complexity: O(2n) 

Space Complexity: O(2n) 

 

CountPathMaze 

Given a 2D grid, find the number of ways to reach (n-1, n-1). 

You can go to (i,j) from (i-1,j) and (i,j-1).  

Time Complexity: O(2n) 

Space Complexity: O(2n) 



  







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