Merge pull request #428 from Shubh-Krishna/main

Completed Day18q3 Palindrome Linked list Day19 q1 Find Players with Zeroes and One and Day 19 q3 Letter Combination of a Phone number

Day-18/q3:Palindrome Linked List/Shubh-Krishna--c.md

@@ -0,0 +1,35 @@
+```
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     ListNode() : val(0), next(nullptr) {}
+ *     ListNode(int x) : val(x), next(nullptr) {}
+ *     ListNode(int x, ListNode *next) : val(x), next(next) {}
+ * };
+ */
+class Solution {
+public:
+    bool isPalindrome(ListNode* head) {
+        ListNode *s=head;
+        int i=0;
+        while (s != nullptr){
+            i++;
+            s=s->next;
+        }
+        s = head;
+        int arr[i];
+        for (int j=0;j<i;j++){
+            arr[j]=s->val;
+            s=s->next;
+        }
+        for (int a = 0, b = i - 1; a < b; a++, b--) {
+            if (arr[a] != arr[b]) {
+                return false;
+            }
+        }
+        return true;
+    }
+};
+```

Day-18/q3:Palindrome Linked List/question.md

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+# Palindrome Linked List
+Given the head of a singly linked list, return true if it is a
+palindrome or false otherwise.
+
+## Example 1:
+Input: head = [1,2,2,1]
+
+Output: true
+
+
+## Example 2:
+
+Input: head = [1,2]
+
+Output: false

Day-19/q1 Find Players With Zero or One Losses/Shubh-Krishna--c.md

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+```
+class Solution {
+public:
+    vector<vector<int>> findWinners(vector<vector<int>>& matches) {
+        map<int, pair<int, int>> mp;
+        for(auto i : matches){
+            mp[i[0]].first++;
+            mp[i[1]].second++;
+        }
+        vector<vector<int>> ans(2);
+        for(auto [i, v] : mp){
+            if(v.second == 0) ans[0].push_back(i);
+            else if(v.second == 1) ans[1].push_back(i);
+        }
+        return ans;
+    }
+};
+```

Day-19/q3-Letter Combinations of a Phone Number/Shubh-Krishna--c.md

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+```
+ 	vector<string> res;
+ 	string key[10] = {"", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
+ public:
+ 	vector<string> letterCombinations(string digits) {
+ 		if(digits.empty()) return res_;
+ 		recur(digits, "", 0);
+ 		return res;
+ 	}
+ 	void recur(string s, string cur, int index){
+ 		if(index == s.length()) res_.emplace_back(cur);
+ 		else{
+ 			string letters = key[s[index] - '0'];
+ 			for(const char c: letters){
+ 				recur(s, cur + c, index + 1);
+ 			}
+ 		}
+ 	}
+```