study

qsort.c

@@ -0,0 +1,123 @@
+#include <stdio.h>
+
+static int qsort_swap(int *a, int *b)
+{
+    int tmp;
+    tmp = *a;
+    *a = *b;
+    *b = tmp;
+
+    return 0;
+}
+
+void qsort(int *base, int nmemb)
+{
+    int *begin_stack[10];
+    int *end_stack[10];
+    int *begin;
+    int *end;
+    int *seg1;
+    int *seg2;
+    int *seg2p;
+    int loop;
+    unsigned int offset;
+
+    /* 使用栈而不是常见的递归实现 */
+    begin_stack[0] = base;      //开始元素位置栈，入栈
+    end_stack[0]   = base + (nmemb - 1) ;   //结束位置栈，入栈
+
+    for (loop = 0; loop >= 0; --loop) {
+        begin = begin_stack[loop];          //开始位置出栈
+        end   = end_stack[loop];        //结束位置出栈
+
+        while (begin < end) {
+            offset = (end - begin) >> 1;        //取中间位置
+
+            qsort_swap(begin, begin + offset);      //交换开始和中间的位置
+
+            for (int i = 0; i < 8;i++) 
+            {
+                printf("%d ", base[i]);
+            }
+            printf("\n\n");
+
+
+            seg1 = begin;
+            seg2 = end;
+
+            while (1) {
+                for (; seg1 < seg2 && *begin < *seg1 ; seg1 += 1);
+
+                for (; seg2 >= seg1 && *seg2 > *begin; seg2 -= 1);
+
+                if (seg1 >= seg2)
+                    break;
+
+                qsort_swap(seg1, seg2);
+
+
+                for (int i = 0; i < 8;i++) 
+                {
+                    printf("%d ", base[i]);
+                }
+                printf("\n\n");
+            }
+
+            qsort_swap(begin, seg2);
+
+
+            for (int i = 0; i < 8;i++) 
+            {
+                printf("%d ", base[i]);
+            }
+            printf("\n\n");
+
+            seg2p = seg2;
+
+            if ((seg2p - begin) <= (end - seg2p)) {
+                if (seg2p < end) {          //右侧入栈
+                    begin_stack[loop] = seg2p + 1;
+                    end_stack[loop++] = end;
+                }
+                end = seg2p;
+            } else {
+                if (seg2p > begin) {        // 左侧入栈
+                    begin_stack[loop] = begin;
+                    end_stack[loop++] = seg2p - 1;
+                }        //end if
+                begin = seg2p;
+            }       //end if
+        }           //end while
+
+
+        for (int i = 0; i < 8;i++) 
+        {
+            printf("%d ", base[i]);
+        }
+        printf("\n\n");
+    }                   //end for
+
+}
+int main(int argc, char *argv[])
+{
+    int a[10] = {14, 5, 7, 8, 2, 4, 55, 3};
+    int i;
+
+    printf("\n\n");
+    for (i = 0; i < 8;i++) 
+    {
+        printf("%d ", a[i]);
+    }
+    printf("\n\n");
+
+    qsort(a, 8);
+
+    printf("\n\n");
+    for (i = 0; i < 8;i++) 
+    {
+        printf("%d ", a[i]);
+    } 
+    printf("\n\n");
+
+    return 0;
+}