50 days coding sheet

Author: ishan.gupta

2sum.cpp

@@ -0,0 +1,21 @@
+using namespace std;
+#include <iostream>
+#include <bits/stdc++.h>
+// remove above lines when running in leetcode. 
+
+class Solution {
+public:
+    vector<int> twoSum(vector<int>& nums, int target) {
+        unordered_map<int,int> umap;
+        for(int i=0;i<nums.size();i++){
+            umap[nums[i]] = i;
+        }
+
+        for(int i=0;i<nums.size();i++){
+            if(umap.find(target-nums[i]) != umap.end() && i!=umap[target-nums[i]]){
+                return {i,umap[target-nums[i]]};
+            }
+        }
+        return {};
+    }
+};

3sum.cpp

@@ -0,0 +1,68 @@
+using namespace std;
+#include <iostream>
+#include <bits/stdc++.h>
+// remove above lines when running in leetcode. 
+
+
+class Solution {
+public:
+    vector<vector<int>> threeSum(vector<int>& nums) {
+        map<vector<int>,int> s;
+        vector<vector<int>> ans;
+        int len = nums.size()-1;
+        int value1,target=0;
+        sort(nums.begin(),nums.end());
+
+        for(int i=0;i<nums.size();i++){
+            value1 = nums[i];
+            target = target - nums[i];
+            int left=i+1  ,right=len;
+            while(left<right){
+                if(nums[left]+nums[right]==target){
+                    vector<int> v({value1,nums[left],nums[right]});
+                    s[v]++;
+                    left++;
+                    right--;
+                } else if(nums[left]+nums[right]>target){
+                    right--;
+                } else {
+                    left++;
+                }
+            }
+            target = 0;
+        }
+        for (auto i : s) {
+            ans.push_back(i.first);
+        }
+
+
+
+        // my first approach- this was right too but was giving TLE.
+        
+        // for(int i=0;i<nums.size();i++){
+        //     value1 = nums[i];
+        //     target = target - nums[i];
+        //     unordered_map<int,int> umap;
+        //     for(int j=i+1;j<nums.size();j++){
+        //             umap[nums[j]] = j;
+        //     }
+        //     for(int j=i+1;j<nums.size();j++){
+        //         if(umap.find(target - nums[j]) != umap.end() && j!=umap[target - nums[j]]){
+        //             value2 = nums[j];
+        //             value3 = target-nums[j];
+        //             vector<int> v({value1,value2,value3});
+        //             sort(v.begin(),v.end());
+        //             // s.insert(v);
+        //             s[v]++;
+        //         }
+        //     }
+        //     target = 0;
+        // }
+        // for (auto i : s) {
+        //     ans.push_back(i.first);
+        // }
+        return ans;
+
+    }
+
+};

4sum.cpp

@@ -0,0 +1,49 @@
+using namespace std;
+#include <iostream>
+#include <bits/stdc++.h>
+// remove above lines when running in leetcode. 
+
+class Solution {
+public:
+    vector<vector<int>> fourSum(vector<int>& nums, int target) {
+        map<vector<int>,int> m;
+        vector<vector<int>> vec;
+        int len = nums.size()-1;
+        long long int actualTarget = target, newTargetI, newTargetJ, finalTarget;
+        int value1, value2;
+        sort(nums.begin(),nums.end());
+        for(int i=0;i<nums.size();i++){
+            value1 = nums[i];
+            newTargetI = target - nums[i];
+            for(int j=i+1;j<nums.size();j++){
+                value2 = nums[j];
+                // newTargetJ = newTargetI;
+                finalTarget = newTargetI-nums[j];
+                int left=j+1  ,right=len;
+                while(left<right){
+                    // cout<<"L-"<<left<<"\n";
+                    // cout<<"R-"<<right<<"\n";
+                    if(nums[left]+nums[right]==finalTarget){
+                        // cout<<"E";
+                        vector<int> v({value1,value2,nums[left],nums[right]});
+                        m[v]++;
+                        left++;
+                        right--;
+                    } else if(nums[left]+nums[right]>finalTarget){
+                        right--;
+                        // cout<<"F";
+                    } else {
+                        left++;
+                        // cout<<"G";
+                    }
+                }
+
+            }
+            target = actualTarget;
+        }
+        for (auto i : m) {
+            vec.push_back(i.first);
+        }
+        return vec;
+    }
+};

maximum_subarray.cpp

@@ -0,0 +1,21 @@
+using namespace std;
+#include <iostream>
+#include <bits/stdc++.h>
+// remove above lines when running in leetcode. 
+
+class Solution {
+public:
+    int maxSubArray(vector<int>& nums) {
+        int max1 = INT_MIN, sum=0;
+        for(int i=0 ; i<nums.size() ;i++ ){
+            sum+=nums[i];
+            if(sum<0){
+                max1 = max(max1,sum);
+                sum = 0;
+            } else {
+                max1 = max(max1,sum);
+            }
+        }
+        return max1;
+    }
+};

sortColors.cpp

@@ -0,0 +1,34 @@
+using namespace std;
+#include <iostream>
+#include <bits/stdc++.h>
+// remove above lines when running in leetcode. 
+
+
+class Solution {
+public:
+    void sortColors(vector<int>& nums) {
+        int left = 0;
+        int right = nums.size()-1;
+        int mid = left;
+
+        while(mid<=right){
+            if(nums[mid]==0){
+                int temp = nums[mid];
+                nums[mid] = nums[left];
+                nums[left] = temp;
+                left++;
+                mid++;
+            }
+            else if(nums[mid]==1){
+                mid++;
+            }
+            else{
+                int temp = nums[mid];
+                nums[mid] = nums[right];
+                nums[right] = temp;
+                right--;
+            }
+        }
+        
+    }
+};