| 1 | import java.util.ArrayList; |
| 2 | |
| 3 | public class Classroom { |
| 4 | //Brute Force |
| 5 | // public static boolean pairSum1(ArrayList<Integer> list, int target) { |
| 6 | |
| 7 | // for(int i=0; i<list.size(); i++) { |
| 8 | // for(int j=i+1; j<list.size(); j++) { |
| 9 | // if(list.get(i) + list.get(j) == target) { |
| 10 | // return true; |
| 11 | // } |
| 12 | // } |
| 13 | // } |
| 14 | |
| 15 | // return false; |
| 16 | // } |
| 17 | |
| 18 | //2 pointer approach |
| 19 | public static boolean pairSum1(ArrayList<Integer> list, int target) { |
| 20 | int lp = 0; |
| 21 | int rp = list.size()-1; |
| 22 | |
| 23 | while(lp != rp) { |
| 24 | //case 1 |
| 25 | if(list.get(lp)+list.get(rp) == target) { |
| 26 | return true; |
| 27 | } |
| 28 | |
| 29 | //case 2 |
| 30 | if(list.get(lp)+list.get(rp) < target) { |
| 31 | lp++; |
| 32 | } else { |
| 33 | //case 3 |
| 34 | rp--; |
| 35 | } |
| 36 | } |
| 37 | |
| 38 | return false; |
| 39 | } |
| 40 | |
| 41 | //O(n) |
| 42 | public static boolean pairSum2(ArrayList<Integer> list, int target) { |
| 43 | int bp = -1; |
| 44 | int n = list.size(); |
| 45 | for(int i=0; i<list.size(); i++) { |
| 46 | if(list.get(i) > list.get(i+1)) { //breaking point |
| 47 | bp = i; |
| 48 | break; |
| 49 | } |
| 50 | } |
| 51 | |
| 52 | int lp = bp+1; //smallest |
| 53 | int rp = bp; //largest |
| 54 | |
| 55 | while(lp != rp) { |
| 56 | //case1 |
| 57 | if(list.get(lp) + list.get(rp) == target) { |
| 58 | return true; |
| 59 | } |
| 60 |
nothing calls this directly
no outgoing calls
no test coverage detected
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