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public class GenerateParentheses {
public List<String> generateParenthesis(int n) {
List<String> result = new ArrayList<String>();
if (n <= 0) {
return result;
}
helper(n, n, new StringBuilder(), result);
return result;
}
private void helper(int left, int right, StringBuilder sb, List<String> result) {
if (left == 0 && right == 0) {
result.add(sb.toString());
return;
}
if (left > right) {
return;
}
if (left > 0) {
StringBuilder sbl = new StringBuilder(sb);
sbl.append('(');
helper(left - 1, right, sbl, result);
}
if (right >= left) {
StringBuilder sbr = new StringBuilder(sb);
sbr.append(')');
helper(left, right - 1, sbr, result);
}
}
@Test
public void test() {
List<String> result = generateParenthesis(3);
}
}
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