Added solutions to selected leetcode problems (#344)

Author: Dadaji18

Maths/nge1_496.cpp

@@ -0,0 +1,25 @@
+class Solution {
+public:
+    vector<int> nextGreaterElement(vector<int>& nums1, vector<int>& nums2) {
+        int n = nums1.size(), m = nums2.size();
+        vector<int> res(n, -1);
+        stack<int> st;
+        unordered_map<int, int> mp;
+        for(int i = 0; i < m; i++){
+            int val = nums2[i];
+            while(!st.empty() and val > st.top()){
+                mp[st.top()] = val;
+                st.pop();
+            }
+            st.push(val);
+        }
+        for(int i = 0; i < n; i++){
+            int val = nums1[i];
+            if(mp.find(val) != mp.end()){
+                int nge = mp[val];
+                res[i] = nge;
+            }
+        }
+        return res;
+    }
+};

Maths/nge2_503.cpp

@@ -0,0 +1,19 @@
+class Solution {
+public:
+    vector<int> nextGreaterElements(vector<int>& nums) {
+        int n = nums.size();
+        vector<int> res(n, -1);
+        stack<int> st;
+        for(int i = 2*n-1; i > -1; i--){
+            while(!st.empty() and nums[i%n] >= st.top()){
+                st.pop();
+            }
+            if(i < n){
+                if(!st.empty())
+                    res[i] = st.top();
+            }
+            st.push(nums[i%n]);
+        }
+        return res;
+    }
+};

Maths/nge3_556.cpp

@@ -0,0 +1,20 @@
+class Solution {
+public:
+    int nextGreaterElement(int num) {
+        vector<int> v;
+        while(num){
+            v.push_back(num%10);
+            num /= 10;
+        }
+        if(is_sorted(v.begin(), v.end()))
+            return -1;
+        reverse(v.begin(), v.end());
+        next_permutation(v.begin(), v.end());
+        long long temp = 0;
+        for(int i = 0; i < v.size(); i++){
+            temp = temp*10 + v[i];
+        }
+        if(temp > INT_MAX) return -1;
+        return temp;
+    }
+};

Maths/reordered_power_of_2_869.cpp

@@ -0,0 +1,17 @@
+class Solution {
+public:
+    bool reorderedPowerOf2(int n) {
+        map<string, int> mp;
+        mp["1"]++;
+        int num = 1;
+        while(mp.size() != 30){
+            num *= 2;
+            string s = to_string(num);
+            sort(s.begin(), s.end());
+            mp[s]++;
+        }
+        string s = to_string(n);
+        sort(s.begin(), s.end());
+        return (mp.find(s) != mp.end());
+    }
+};

Maths/xor_sum_of_all_pairs_and_1835.cpp

@@ -0,0 +1,11 @@
+class Solution {
+public:
+    int getXORSum(vector<int>& arr1, vector<int>& arr2) {
+        int a = 0, b = 0;
+        for(auto i : arr1)
+            a = a ^ i;
+        for(auto j : arr2)
+            b = b ^ j;
+        return a & b;
+    }
+};