update problems

Author: Fettes

Array/1.two-sum.java

@@ -0,0 +1,23 @@
+/*
+ * @lc app=leetcode id=1 lang=java
+ *
+ * [1] Two Sum
+ */
+
+// @lc code=start
+class Solution {
+    public int[] twoSum(int[] nums, int target) {
+        Map<Integer, Integer> map = new HashMap<>();
+        
+        for (int i = 0; i < nums.length; i++) {
+            int sum = target - nums[i];
+            if (map.containsKey(sum)) {
+                return new int[]{i, map.get(sum)};
+            }
+            map.put(nums[i], i);
+        }
+        return new int[]{};
+    }
+}
+// @lc code=end
+

Array/15.3-sum.java

@@ -0,0 +1,41 @@
+/*
+ * @lc app=leetcode id=15 lang=java
+ *
+ * [15] 3Sum
+ */
+
+// @lc code=start
+class Solution {
+    public List<List<Integer>> threeSum(int[] nums) {
+        List<List<Integer>> result = new ArrayList<>();
+
+        if (nums.length == 0) {
+            return result;
+        }
+        Arrays.sort(nums);
+        for (int i = 0; i < nums.length; i++) {
+            if (i > 0 && nums[i] == nums[i - 1]) continue;
+            int left = i + 1;
+            int right = nums.length - 1;
+
+            while (left < right) {
+                if (nums[i] + nums[left] + nums[right] == 0) {
+                    result.add(new ArrayList<>(Arrays.asList(nums[i], nums[left], nums[right])));
+                    while (left < right && nums[left] == nums[left + 1]) left++;
+                    while (left < right && nums[right] == nums[right - 1]) right--;
+                    left++;
+                    right--;
+                } else if (nums[i] + nums[left] + nums[right] < 0) {
+                    while (left < right && nums[left] == nums[left + 1]) left++;
+                    left++;
+                } else {
+                    while (left < right && nums[right] == nums[right - 1]) right--;
+                    right--;
+                }
+            }
+        }
+        return result;
+    }
+}
+// @lc code=end
+

Array/16.3-sum-closest.java

@@ -0,0 +1,38 @@
+/*
+ * @lc app=leetcode id=16 lang=java
+ *
+ * [16] 3Sum Closest
+ */
+
+// @lc code=start
+class Solution {
+    public int threeSumClosest(int[] nums, int target) {
+        Arrays.sort(nums);
+        
+        int resultSum = 0;
+        int closest = Integer.MAX_VALUE;
+
+        for (int i = 0; i < nums.length; i++) {
+            int low = i + 1;
+            int high = nums.length - 1;
+
+            if (i > 0 && nums[i] == nums[i - 1]) continue;
+            
+            while (low < high) {
+                int tempSum = nums[i] + nums[low] + nums[high];
+                if (tempSum == target) {
+                    return target;
+                } else if (tempSum < target) {
+                    low++;
+                } else {
+                    high--;
+                }
+                resultSum = closest < Math.abs(target - tempSum) ? resultSum : tempSum;
+                closest = Math.min(closest, Math.abs(target - tempSum));
+            }
+        }
+        return resultSum;
+    }
+}
+// @lc code=end
+

Array/259.3-sum-smaller.java

@@ -0,0 +1,29 @@
+/*
+ * @lc app=leetcode id=259 lang=java
+ *
+ * [259] 3Sum Smaller
+ */
+
+// @lc code=start
+class Solution {
+    public int threeSumSmaller(int[] nums, int target) {
+        Arrays.sort(nums);
+        int count = 0;
+        for (int i = 0; i < nums.length; i++) {
+            int low = i + 1;
+            int high = nums.length - 1;  
+
+            while (low < high) {
+                int tempSum = nums[i] + nums[low] + nums[high];
+                if (tempSum < target) {
+                    count += high - low;
+                    low++;
+                } else {
+                    high--;
+                }
+            }
+        }
+        return count;
+    }
+}
+// @lc code=end