for(int i =0 ; i<rrs.length() ; i++) {
mr.add(rrs.substring(0, i) + cc + rrs.substring(i));
}
suppose “cc” here is ‘a’…and rrs for the time being is ‘bc’…now if rrs.length() is 2,this means the loop shall run for 2 times…but then how come the answer is coming out to be abc,bac,bca which is possible onlyif the loop runs for 3 times
package recursionquestions; import java.util.ArrayList; public class Recursion { public static void main(String[] args) { System.out.println(getPermutations(“abc”)); } public static ArrayList getSS(String str){ if(str.length() == 0 ) { ArrayList br = new ArrayList<>(); br.add(" “); return br; } char cc = str.charAt(0); String a = str.substring(1); ArrayList rr = getSS(a); ArrayList mr = new ArrayList<>(); for(int i=0 ; i<rr.size() ; i++) { mr.add(rr.get(i)); mr.add(cc + rr.get(i)); } return mr; } public static ArrayList getPermutations(String str){ if(str.length() == 0) { ArrayList br = new ArrayList<>(); br.add(” "); return br; } char cc = str.charAt(0); String a = str.substring(1); ArrayList mr = new ArrayList<>(); ArrayList rr = getPermutations(a); for(String rrs:rr) { for(int i =0 ; i<rrs.length() ; i++) { mr.add(rrs.substring(0, i) + cc + rrs.substring(i)); } } return mr; } }
for (String rrs : rr) {
for (int i = 0; i < rrs.length(); i++) {
mr.add(rrs.substring(0, i) + cc + rrs.substring(i));
}
}
Look at this code. If cc is a, then rr = [bc , cb ]
Now for rrs = bc
when i = 0, mr.add("" + “a” + “bc”) , thus abc will be added to mr.
when i = 1, mr.add(“b” + “a” + “c”), thus bac will be added to mr.
when i=2, mr.add(“bc” + “a” + “”), thus bca will be added to mr.
Here the length of "bc " is 3 because there is a " " char at the end. Hence the loop runs 3 times.
@himanshuep32,
Also, I have corrected your code: https://ide.codingblocks.com/s/209329
Whenever you use Arraylist put the parameter as well. Parameter defines the values it will store. For arraylist of strings use ArrayList
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