[chjung99] WEEK 05 solutions

3sum/chjung99.java

@@ -0,0 +1,48 @@
+// two pointer
+// time: O(N^2)
+// space: O(N)
+
+class Solution {
+    Set<List<Integer>> set = new HashSet<>();
+    public List<List<Integer>> threeSum(int[] nums) {
+        Arrays.sort(nums);
+
+        for (int i = 0; i < nums.length; i++){
+            twoSum(nums, i);
+        }
+
+        return new ArrayList<>(set);
+    }
+    public void twoSum(int[] nums, int targetIdx){
+        int left = 0;
+        int right = nums.length - 1;
+
+        while (left < right) {
+            if (left == targetIdx){
+                left ++;
+                continue;
+            }
+            if (right == targetIdx){
+                right--;
+                continue;
+            }
+            if (nums[left] + nums[right] == -nums[targetIdx]) {
+                if (nums[left] > nums[targetIdx]){
+                    set.add(List.of(nums[targetIdx], nums[left], nums[right]));
+                }
+                else if (nums[targetIdx] > nums[right]){
+                    set.add(List.of(nums[left],nums[right],nums[targetIdx]));
+                } else{
+                    set.add(List.of(nums[left], nums[targetIdx], nums[right]));
+                }
+                left++;
+            } else if (nums[left] + nums[right] < -nums[targetIdx]){
+                left ++;
+            } else {
+                right --;
+            }
+        }
+    }
+}
+
+

combination-sum/chjung99.java

@@ -0,0 +1,29 @@
+class Solution {
+    Set<List<Integer>> combination = new HashSet<>();
+    public List<List<Integer>> combinationSum(int[] candidates, int target) {
+        Arrays.sort(candidates);
+        findCombination(candidates, target, 0, 0, new ArrayList<>());
+        return new ArrayList<>(combination);
+    }
+
+    public void findCombination(int[] candidates, int target, int curIdx, int curSum, List<Integer> curList) {
+        if (curSum == target) {
+            combination.add(new ArrayList<>(curList));
+            return;
+        }
+
+        if (curSum > target) {
+            return;
+        }
+
+        for (int i = curIdx; i < candidates.length; i++){
+
+            curList.add(candidates[i]);
+            findCombination(candidates, target, i, curSum + candidates[i], curList);
+            curList.remove(curList.size()-1);
+        }
+    }
+}
+
+
+

container-with-most-water/chjung99.java

@@ -0,0 +1,27 @@
+// two pointer
+// time: O(N)
+// space: O(1)
+class Solution {
+    public int maxArea(int[] height) {
+        int left = 0;
+        int right = height.length-1;
+        int answer = 0;
+
+        int waterWidth = 0;
+        int waterHeight = 0;
+
+        while (left < right){
+            waterWidth = (right - left);
+            waterHeight = Math.min(height[left], height[right]);
+            answer = Math.max(answer, waterWidth * waterHeight);
+            if (height[left] <= height[right]) {
+                left ++;
+            }else{
+                right --;
+            }
+        }
+
+        return answer;
+    }
+}
+

remove-nth-node-from-end-of-list/chjung99.java

@@ -0,0 +1,48 @@
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode() {}
+ *     ListNode(int val) { this.val = val; }
+ *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
+ * }
+ */
+class Solution {
+    public ListNode removeNthFromEnd(ListNode head, int n) {
+        int size = getSizeOfListNode(head);
+
+        if (size - n - 1 >= 0) {
+            ListNode prev = moveNth(head, size - n - 1);
+            ListNode target = moveNth(head, size - n);
+            prev.next = target.next;
+        } else {
+            head = head.next;
+        }
+
+
+        return head;
+    }
+    public ListNode moveNth(ListNode head, int n){
+        while (head != null){
+            if (n == 0) break;
+            head = head.next;
+            n--;
+        }
+        return head;
+    }
+    public void removeNth(ListNode head, int n){
+        int cnt = n;
+
+    }
+    public int getSizeOfListNode(ListNode head){
+        int size = 0;
+        while (head != null) {
+            size ++;
+            head = head.next;
+        }
+        return size;
+    }
+}
+
+

search-in-rotated-sorted-array/chjung99.java

@@ -0,0 +1,49 @@
+class Solution {
+    public int search(int[] nums, int target) {
+        int leftSide = 0;
+        int rightSide = nums.length - 1;
+        int left = 0;
+        int right = nums.length;
+        int mid;
+
+        if (nums.length == 1) {
+            if (nums[0] == target) return 0;
+            else return -1;
+        }
+
+        while (left + 1 < right) {
+            mid = (int) (left + right) / 2;
+
+            if (nums[mid]==target) {
+                break;
+            }
+            else if (nums[mid] < target){ // 값이 증가해야함
+                if (nums[mid] >= nums[leftSide]){ // 왼쪽 그룹에 속하는 지
+                    left = mid;
+                } else { // 오른쪽 그룹에 속하는 지
+                    if (nums[rightSide] < target) {
+                        right = mid;
+                    } else {
+                        left = mid;
+                    }
+                }
+            } else{ // nums[mid] > target // 값이 감소해야함
+                if (nums[mid] >= nums[leftSide]){ // 왼쪽 그룹에 속하는 지
+                    if (nums[leftSide] <= target) {
+                        right = mid;
+                    } else {
+                        left = mid;
+                    }
+                } else { // 오른쪽 그룹에 속하는 지
+                    right = mid;
+                }
+
+            }
+        }
+        mid = (int)((left + right) / 2);
+        if (nums[mid]==target) return mid;
+        else return -1;
+    }
+}
+
+