Create Combinations.cpp

Author: akashmodak97

Leet Code/Combinations.cpp

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+/* Leet Code */
+/* Title - Combinations */
+/* Created By - Akash Modak */
+/* Date - 06/06/2023 */
+
+// Given two integers n and k, return all possible combinations of k numbers chosen from the range [1, n].
+
+// You may return the answer in any order.
+
+ 
+
+// Example 1:
+
+// Input: n = 4, k = 2
+// Output: [[1,2],[1,3],[1,4],[2,3],[2,4],[3,4]]
+// Explanation: There are 4 choose 2 = 6 total combinations.
+// Note that combinations are unordered, i.e., [1,2] and [2,1] are considered to be the same combination.
+// Example 2:
+
+// Input: n = 1, k = 1
+// Output: [[1]]
+// Explanation: There is 1 choose 1 = 1 total combination.
+
+class Solution {
+public:
+    void backtrack(int i, int j, int k, int n, vector<int> &temp, vector<vector<int>> & res){
+        if(i==k){
+            res.push_back(temp);
+            return;
+        }
+        for(int l=j;l<=n;l++){
+            temp.push_back(l);
+            j++;
+            backtrack(i+1,j,k,n,temp,res);
+            temp.pop_back();
+        }
+
+    }
+    vector<vector<int>> combine(int n, int k) {
+        vector<int> temp;
+        vector<vector<int>> res;
+        backtrack(0,1,k,n,temp,res);
+        return res;
+    }
+};