From dc1fa3f381c9d98ea832036e5b355f031adc763b Mon Sep 17 00:00:00 2001
From: Tomasz Polgrabia <tomasz@polgrabia.me>
Date: Sat, 8 Feb 2025 22:23:00 +0100
Subject: [PATCH] Added hoare algorithm.
---
current/algorithms/hoare.c | 120 +++++++++++++++++++++++++++++++++++++
1 file changed, 120 insertions(+)
create mode 100644 current/algorithms/hoare.c
diff --git a/current/algorithms/hoare.c b/current/algorithms/hoare.c
new file mode 100644
index 0000000..be0bf1a
--- /dev/null
+++ b/current/algorithms/hoare.c
@@ -0,0 +1,120 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+
+int hoare(int* arr, int i, int j, int idx) {
+ printf("I: %d, J: %d, IDX: %d\n", i, j, idx);
+ if (idx < i) {
+ return 0xdeadbeef;
+ }
+
+ if (idx > j) {
+ return 0xdeadbeef;
+ }
+
+ int v;
+ int x1,x2;
+ int t;
+ while (i < j - 1) {
+ v = arr[(i + j) / 2];
+ printf("Round: (%d,%d) - v: %d\n", i, j, v);
+ // sorting on three partitions
+
+ x1 = i;
+ x2 = j;
+
+ while (x1 < x2) {
+
+ while (x1 < x2 && arr[x1] <= v) {
+ printf("x1: %d, arr[x1]: %d\n", x1, arr[x1]);
+ x1++;
+ }
+
+ while (x1 < x2 && arr[x2] > v) {
+ printf("x2: %d, arr[x2]: %d\n", x2, arr[x2]);
+ x2--;
+ }
+
+ printf("X1 %d to swap %d\n", x1, arr[x1]);
+ printf("X2 %d to swap %d\n", x2, arr[x2]);
+
+ // if x1 == x2, the change makes no difference
+
+ t = arr[x1];
+ arr[x1] = arr[x2];
+ arr[x2] = t;
+
+ }
+
+ if (arr[x1] > v) x1--; // we could cross == element by
+
+ x2 = x1;
+ x1 = i;
+
+ while (x1 < x2) {
+
+ while (x1 < x2 && arr[x1] < v) {
+ printf("x1: %d, arr[x1]: %d\n", x1, arr[x1]);
+ x1++;
+ }
+
+ while (x1 < x2 && arr[x2] == v) {
+ printf("x2: %d, arr[x2]: %d\n", x2, arr[x2]);
+ x2--;
+ }
+
+ printf("X1 %d to swap %d\n", x1, arr[x1]);
+ printf("X2 %d to swap %d\n", x2, arr[x2]);
+
+ // if x1 == x2, the change makes no difference
+
+ t = arr[x1];
+ arr[x1] = arr[x2];
+ arr[x2] = t;
+
+ }
+
+ if (x1 > idx) {
+ printf("Changing j %d to %d\n", j, x1);
+ j = x1;
+ } else {
+ // x1 <= idx
+ printf("Changing i %d to %d\n", i, x1);
+ i = x1;
+ }
+ }
+
+ // we should have i == j == idx
+ printf("i: %d, j: %d, idx: %d, v: %d\n", i, j, idx, arr[idx]);
+ return arr[idx]; // in order to make it work, we need to make sure that in this place is fully sorted, one way is to split into three pieces
+}
+
+/**
+ * n: 4
+ * 4
+ * 3
+ * 2
+ * 1
+ * idx: 4, 3, 2, 1 all work
+ */
+
+int main() {
+
+ int n;
+ printf("Provide n: ");
+ scanf("%d", &n);
+
+ int numbers[n];
+
+ for (int i = 0; i < n; i++) {
+ scanf("%d", &numbers[i]);
+ }
+
+ int idx;
+ printf("Idx: ");
+ scanf("%d", &idx);
+
+ int res = hoare(numbers, 0, n-1, idx);
+ printf("Res: %x\n", res);
+ return 0;
+}