add

public/c/ch2/halfsearch/fenzhi.c

@@ -0,0 +1,28 @@
+#include <stdio.h>
+
+int binarySearch(int a[], int size, int key) {
+    int left = 0;
+    int right = size - 1;
+    while (left <= right) {
+        int middle = (left + right) / 2;
+        if (key == a[middle])
+            return middle;
+        else if (key > a[middle])
+            left = middle + 1;
+        else
+            right = middle - 1;
+    }
+    return -1;
+}
+
+int main() {
+    int a[] = {1, 3, 5, 7, 9};
+    int size = sizeof(a) / sizeof(a[0]);
+    int key = 7;
+    int index = binarySearch(a, size, key);
+    if (index != -1)
+        printf("元素索引是 %d\n", index);
+    else
+        printf("没有找到\n");
+    return 0;
+}

public/c/ch2/halfsearch/fenzhirec.c

@@ -0,0 +1,26 @@
+#include <stdio.h>
+int RecursionHalfSearch(int a[], int left, int right, int key) {
+    if (left <= right) {
+        int middle = (left + right) / 2;
+        if (key == a[middle])
+            return middle;
+        else if (key > a[middle])
+            return RecursionHalfSearch(a, middle + 1, right, key);
+        else
+            return RecursionHalfSearch(a, left, middle - 1, key);
+    } else {
+        return -1;
+    }
+}
+
+int main() {
+    int a[] = {1, 3, 5, 7, 9};
+    int size = sizeof(a) / sizeof(a[0]);
+    int key = 7;
+    int index = RecursionHalfSearch(a, 0, size - 1, key);
+    if (index != -1)
+        printf("Element found at index %d\n", index);
+    else
+        printf("Element not found\n");
+    return 0;
+}