Merge pull request deutranium#194 from rcchcz/shellSortCPP

ShellSort in C++

Author: deutranium

sortingAlgo/ShellSort/ShellSort.cpp

@@ -0,0 +1,51 @@
+#include <vector>
+#include <algorithm>
+#include <iostream>
+
+/**
+ * This function implements the Shell Sorting Algorithm.
+ * 
+ * @note Knuth sequence was used.
+ * 
+ * @param v Vector to be sorted.
+ */
+void shellSort(std::vector<int> &v) { 
+    int gap;
+    // calculate the first gap, based on Knuth sequence
+    for(gap = 1; gap < (v.end() - v.begin()); gap = 3 * gap + 1); 
+    while(gap > 0) { // change to while(gap)
+        // descrease the gap
+        gap = (gap - 1)/3;
+        // pass by elements to swap then if necessary
+        for(size_t i = 0; v.begin() + gap + i < v.end(); i++) {
+            if(*(v.begin() + gap + i) < *(v.begin() + i)) {
+                std::swap(*(v.begin() + gap + i), *(v.begin() + i));
+                // in case some element was sawpped, it will try swap the elements before, maintaining the gap
+                for(int j = i - gap; j >= 0; j -= gap) {   
+                    if(*(v.begin() + gap + j) < *(v.begin() + j)) { std::swap(*(v.begin() + gap + j), *(v.begin() + j)); }         
+                }
+            }
+        }
+        
+    }
+}
+
+/**
+ * Simple print function.
+ */
+void printVec(std::vector<int> v) {  
+    for(int i = 0; i < v.size(); i++) std::cout << v[i] << " "; 
+    std::cout << std::endl; 
+} 
+
+/**
+ * Driver code.
+ */ 
+int main() {  
+    std::vector<int> v = {23, -10, 20, -11, 12, -6, 7, 299, 9, -1, 37, 51, 0};      
+    shellSort(v);
+    std::cout << "Sorted: ";
+    printVec(v); 
+    
+    return 0;  
+}