Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.
For example, given n = 3, a solution set is:
"((()))", "(()())", "(())()", "()(())", "()()()"
public List<String> generateParenthesis(int n) { char[] pars = new char[n*2]; List<String> result = new ArrayList<>(); generate(result, n, n, pars, 0); return result; } private void generate(List<String> result, int l, int r, char[] pars, int index) { if(l>r) return; if(r==0) { result.add(new String(pars)); return; } if(l>0) { pars[index] = '('; generate(result, l-1, r, pars, index+1); } if(r>l) { pars[index] = ')'; generate(result, l, r-1, pars, index+1); } }