Added 4sum

Author: gahogg

4Sum - Leetcode 18/4Sum - Leetcode 15.cpp

@@ -0,0 +1,38 @@
+#include <vector>
+#include <algorithm>
+
+using namespace std;
+
+class Solution {
+public:
+    vector<vector<int>> fourSum(vector<int>& nums, int target) {
+        vector<vector<int>> answer;
+        sort(nums.begin(), nums.end());
+        int n = nums.size();
+
+        for (int i = 0; i < n; i++) {
+            if (i > 0 && nums[i] == nums[i - 1]) continue;
+
+            for (int j = i + 1; j < n; j++) {
+                if (j > i + 1 && nums[j] == nums[j - 1]) continue;
+
+                int lo = j + 1, hi = n - 1;
+                while (lo < hi) {
+                    long long sum = (long long)nums[i] + nums[j] + nums[lo] + nums[hi];
+                    if (sum == target) {
+                        answer.push_back({nums[i], nums[j], nums[lo], nums[hi]});
+                        lo++;
+                        hi--;
+                        while (lo < hi && nums[lo] == nums[lo - 1]) lo++;
+                        while (lo < hi && nums[hi] == nums[hi + 1]) hi--;
+                    } else if (sum < target) {
+                        lo++;
+                    } else {
+                        hi--;
+                    }
+                }
+            }
+        }
+        return answer;
+    }
+};

4Sum - Leetcode 18/4Sum - Leetcode 15.java

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+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+public class Solution {
+    public List<List<Integer>> fourSum(int[] nums, int target) {
+        List<List<Integer>> answer = new ArrayList<>();
+        Arrays.sort(nums);
+        int n = nums.length;
+
+        for (int i = 0; i < n; i++) {
+            if (i > 0 && nums[i] == nums[i - 1]) continue;
+
+            for (int j = i + 1; j < n; j++) {
+                if (j > i + 1 && nums[j] == nums[j - 1]) continue;
+
+                int lo = j + 1, hi = n - 1;
+                while (lo < hi) {
+                    long sum = (long) nums[i] + nums[j] + nums[lo] + nums[hi];
+                    if (sum == target) {
+                        answer.add(Arrays.asList(nums[i], nums[j], nums[lo], nums[hi]));
+                        lo++;
+                        hi--;
+                        while (lo < hi && nums[lo] == nums[lo - 1]) lo++;
+                        while (lo < hi && nums[hi] == nums[hi + 1]) hi--;
+                    } else if (sum < target) {
+                        lo++;
+                    } else {
+                        hi--;
+                    }
+                }
+            }
+        }
+        return answer;
+    }
+}

4Sum - Leetcode 18/4Sum - Leetcode 15.js

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+var fourSum = function(nums, target) {
+    let answer = [];
+    nums.sort((a, b) => a - b);
+    let n = nums.length;
+
+    for (let i = 0; i < n; i++) {
+        if (i > 0 && nums[i] === nums[i - 1]) continue;
+
+        for (let j = i + 1; j < n; j++) {
+            if (j > i + 1 && nums[j] === nums[j - 1]) continue;
+
+            let lo = j + 1, hi = n - 1;
+            while (lo < hi) {
+                let sum = nums[i] + nums[j] + nums[lo] + nums[hi];
+                if (sum === target) {
+                    answer.push([nums[i], nums[j], nums[lo], nums[hi]]);
+                    lo++;
+                    hi--;
+                    while (lo < hi && nums[lo] === nums[lo - 1]) lo++;
+                    while (lo < hi && nums[hi] === nums[hi + 1]) hi--;
+                } else if (sum < target) {
+                    lo++;
+                } else {
+                    hi--;
+                }
+            }
+        }
+    }
+    return answer;
+};

4Sum - Leetcode 18/4Sum - Leetcode 15.py

@@ -0,0 +1,33 @@
+class Solution:
+    def fourSum(self, nums: List[int], target: int) -> List[List[int]]:
+        n = len(nums)
+        answer = []
+        nums.sort()
+
+        for i in range(n):
+            if i > 0 and nums[i] == nums[i-1]:
+                continue
+
+            for j in range(i+1, n):
+                if j > i + 1 and nums[j] == nums[j-1]:
+                    continue
+
+                lo, hi = j + 1, n - 1
+                while lo < hi:
+                    summ = nums[i] + nums[j] + nums[lo] + nums[hi]
+                    if summ == target:
+                        answer.append([nums[i], nums[j], nums[lo], nums[hi]])
+                        lo += 1
+                        hi -= 1
+                        while lo < hi and nums[lo] == nums[lo - 1]:
+                            lo += 1
+                        while lo < hi and nums[hi] == nums[hi + 1]:
+                            hi -= 1
+                    elif summ < target:
+                        lo += 1
+                    else:
+                        hi -= 1
+
+        return answer
+	# Time: O(n^3)
+	# Space: O(n)