0077 new algo added.

0077-Combinations/cpp-0077/CMakeLists.txt

@@ -1,7 +1,6 @@
-cmake_minimum_required(VERSION 3.5)
+cmake_minimum_required(VERSION 3.13)
 project(cpp_0077)
 
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
+set(CMAKE_CXX_STANDARD 14)
 
-set(SOURCE_FILES main.cpp)
-add_executable(cpp_0077 ${SOURCE_FILES})
+add_executable(cpp_0077 main3.cpp)

0077-Combinations/cpp-0077/main.cpp

@@ -7,10 +7,12 @@
 
 using namespace std;
 
+
 /// Naive Recursive
-/// Time Complexity: O(n^k)
+/// Time Complexity: O(k * C(n, k))
 /// Space Complexity: O(k)
 class Solution {
+
 private:
     vector<vector<int>> res;
 
@@ -29,6 +31,7 @@ class Solution {
 
         return;
     }
+
 public:
     vector<vector<int>> combine(int n, int k) {
 
@@ -44,7 +47,7 @@ class Solution {
 };
 
 
-void printVec(const vector<int>& vec){
+void print_vec(const vector<int>& vec){
 
     for(int e: vec)
         cout << e << " ";
@@ -55,6 +58,6 @@ int main() {
 
     vector<vector<int>> res = Solution().combine(4,2);
     for( int i = 0 ; i < res.size() ; i ++ )
-        printVec(res[i]);
+        print_vec(res[i]);
     return 0;
 }

0077-Combinations/cpp-0077/main2.cpp

@@ -7,10 +7,12 @@
 
 using namespace std;
 
+
 /// Naive Recursive Optimized
-/// Time Complexity: O(n^k)
+/// Time Complexity: O(k * C(n, k))
 /// Space Complexity: O(k)
 class Solution {
+
 private:
     vector<vector<int>> res;
 
@@ -30,6 +32,7 @@ class Solution {
 
         return;
     }
+
 public:
     vector<vector<int>> combine(int n, int k) {
 
@@ -45,7 +48,7 @@ class Solution {
 };
 
 
-void printVec(const vector<int>& vec){
+void print_vec(const vector<int>& vec){
 
     for(int e: vec)
         cout << e << " ";
@@ -56,6 +59,6 @@ int main() {
 
     vector<vector<int>> res = Solution().combine(4,2);
     for( int i = 0 ; i < res.size() ; i ++ )
-        printVec(res[i]);
+        print_vec(res[i]);
     return 0;
 }

0077-Combinations/cpp-0077/main3.cpp

@@ -0,0 +1,57 @@
+/// Source : https://leetcode.com/problems/combinations/description/
+/// Author : liuyubobobo
+/// Time   : 2019-03-29
+
+#include <iostream>
+#include <vector>
+
+using namespace std;
+
+
+/// Using bit mask
+/// Time Complexity: O(2^n * n)
+/// Space Complexity: O(1)
+class Solution {
+
+public:
+    vector<vector<int>> combine(int n, int k) {
+
+        vector<vector<int>> res;
+
+        int LIMIT = (1 << n);
+        for(int i = 0; i < LIMIT; i ++){
+
+            vector<int> tres = get_vector(i);
+            if(tres.size() == k) res.push_back(tres);
+        }
+        return res;
+    }
+
+private:
+    vector<int> get_vector(int num){
+
+        vector<int> res;
+        int i = 1;
+        while(num){
+            if(num % 2) res.push_back(i);
+            i ++, num /= 2;
+        }
+        return res;
+    }
+};
+
+
+void print_vec(const vector<int>& vec){
+
+    for(int e: vec)
+        cout << e << " ";
+    cout << endl;
+}
+
+int main() {
+
+    vector<vector<int>> res = Solution().combine(4,2);
+    for( int i = 0 ; i < res.size() ; i ++ )
+        print_vec(res[i]);
+    return 0;
+}