From b2074c035182e2eb8275c1f447354a3afb46cf45 Mon Sep 17 00:00:00 2001
From: ergz <emnlrodriuez@gmail.com>
Date: Fri, 7 Jul 2023 21:24:18 -0700
Subject: [PATCH] redo qs to make sure I get it

---
 c/qs2.cpp | 69 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)
 create mode 100644 c/qs2.cpp

diff --git a/c/qs2.cpp b/c/qs2.cpp
new file mode 100644
index 0000000..816233b
--- /dev/null
+++ b/c/qs2.cpp
@@ -0,0 +1,69 @@
+#include <stdio.h>
+
+/* a rewrite to make sure I can do this without reading */
+
+/*
+partition
+
+Modifies array by moving all values less then a pivot point
+to the left of it and all value greater to the right. Returns
+the index of the pivot at the end of the process.
+
+@param int arr[] array to partition
+@param int lo low value to start iteration on
+@param int hi high value to end iteration on
+ */
+int partition(int arr[], int lo, int hi) {
+    int pindex = lo - 1;        // where pivot will end up
+    int pivot_value = arr[hi];  // can be different
+
+    for (int i = lo; i < hi; i++) {
+        if (arr[i] <= pivot_value) {
+            pindex++;
+            int temp = arr[i];
+            arr[i] = arr[pindex];
+            arr[pindex] = temp;
+        }
+    }
+
+    // after iterating through array, we place pivot in correct
+    // position
+    pindex++;
+    arr[hi] = arr[pindex];
+    arr[pindex] = pivot_value;
+
+    return (pindex);
+}
+
+/*
+quick_sort
+
+@param int arr[] array to be sorted
+@param int lo starting point for iteration
+@param int hi ending point for itereation
+ */
+void quick_sort(int arr[], int lo, int hi) {
+    if (lo < hi) {  // base case is lo == hi
+        int pivot_index = partition(arr, lo, hi);
+
+        quick_sort(arr, lo, pivot_index - 1);
+        quick_sort(arr, pivot_index + 1, hi);
+    }
+}
+
+void print_array(int arr[], int len) {
+    printf("[ ");
+    for (int i = 0; i < len; i++) {
+        printf("%d ", arr[i]);
+    }
+    printf("]\n");
+}
+
+int main() {
+    int arr[5] = {5, 4, 3, 2, 1};
+    printf("before ");
+    print_array(arr, 5);
+    quick_sort(arr, 0, 4);
+    printf("after ");
+    print_array(arr, 5);
+}
\ No newline at end of file