commit bcd520ef121f0f47b16393ab7861b8219b56c01c
Author: xw_y_am <xw_y_am@163.com>
Date:   Tue Jan 15 23:58:49 2019 +0800

    init with old from practice

diff --git a/old/circularly_single_linked_list_stack.c b/old/circularly_single_linked_list_stack.c
new file mode 100644
index 0000000..3041c17
--- /dev/null
+++ b/old/circularly_single_linked_list_stack.c
@@ -0,0 +1,103 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+
+typedef struct _st_node {
+    int val;
+    struct _st_node *next;
+} st_node;
+
+typedef struct {
+    st_node *tail;
+} st_stack;
+
+
+void stack_destroy(st_stack *stack)
+{
+    if (stack->tail) {
+        st_node *p = stack->tail->next;
+        stack->tail->next = 0;
+        for (; p; p = p->next) free(p);
+        stack->tail = 0;
+    }
+}
+
+
+int stack_push(st_stack *stack, int value)
+{
+    st_node *p = (st_node *)malloc(sizeof (st_node));
+    if (!p) return -1;
+
+    if (stack->tail) {
+        p->next = stack->tail->next;
+        stack->tail->next = p;
+    } else {
+        p->next = p;
+    }
+
+    p->val = value;
+    stack->tail = p;
+    return 0;
+}
+
+
+int stack_pop(st_stack *stack, int *value)
+{
+    st_node *p = stack->tail;
+    if (!p) return -1;
+
+    *value = p->val;
+
+    if (p->next == p) {
+        free(p);
+        stack->tail = 0;
+    } else {
+        while (p->next != stack->tail) p = p->next;
+        p->next = p->next->next;
+        free(stack->tail);
+        stack->tail = p;
+    }
+    return 0;
+}
+
+
+void stack_dump(st_stack *stack)
+{
+    printf("stack: [");
+    if (stack->tail) {
+        st_node *p = stack->tail->next;
+        for (; p != stack->tail; p = p->next) printf("%d, ", p->val);
+        printf("%d]\n", p->val); 
+    } else {
+        printf("]\n");
+    }
+}
+
+
+int main()
+{
+    st_stack stack = {0};
+    int get;
+
+    stack_push(&stack, 5);
+    stack_push(&stack, 6);
+    stack_push(&stack, 7);
+    stack_push(&stack, 8);
+    stack_dump(&stack);
+
+    stack_pop(&stack, &get);
+    printf("pop: %d\n", get);
+    stack_pop(&stack, &get);
+    printf("pop: %d\n", get);
+    stack_dump(&stack);
+
+    stack_push(&stack, 10);
+    stack_push(&stack, 11);
+    stack_push(&stack, 12);
+    stack_dump(&stack);
+
+    stack_destroy(&stack);
+    stack_dump(&stack);
+
+    return 0;
+}
diff --git a/old/cpp_class/main.cpp b/old/cpp_class/main.cpp
new file mode 100644
index 0000000..184dd0c
--- /dev/null
+++ b/old/cpp_class/main.cpp
@@ -0,0 +1,17 @@
+
+#include "test.h"
+#include <iostream>
+
+using namespace std;
+
+int main()
+{
+  test t( 3 );
+  cout << t.getval() << endl;
+
+  t.setval( 5 );
+  cout << t.getval() << endl;
+
+  return 0;
+}
+
diff --git a/old/cpp_class/test.cpp b/old/cpp_class/test.cpp
new file mode 100644
index 0000000..ffd6095
--- /dev/null
+++ b/old/cpp_class/test.cpp
@@ -0,0 +1,20 @@
+
+#include "test.h"
+
+test::test( int val )
+{
+  setval( val );
+}
+
+
+void test::setval( int val )
+{
+  this->val = val;
+}
+
+
+int test::getval()
+{
+  return this->val;
+}
+
diff --git a/old/cpp_class/test.h b/old/cpp_class/test.h
new file mode 100644
index 0000000..07efa5b
--- /dev/null
+++ b/old/cpp_class/test.h
@@ -0,0 +1,13 @@
+
+class test {
+
+  public:
+    test( int val );
+    void setval( int val );
+    int getval();
+
+  private:
+    int val;
+
+};
+
diff --git a/old/pc.c b/old/pc.c
new file mode 100644
index 0000000..03689ba
--- /dev/null
+++ b/old/pc.c
@@ -0,0 +1,55 @@
+#include <stdio.h>
+
+long long mod_rev(long long x, long long mod)
+{
+    long long i = 0;
+    long long a = x;
+    long long b = mod;
+    long long pa[3] = {0, 1, 0};
+    long long pb[3] = {0, 0, 1};
+
+    for (;;) {
+        long long q = a / b;
+        long long r = a % b;
+        pa[i] = pa[(i + 1) % 3] - q * pa[(i + 2) % 3];
+        pb[i] = pb[(i + 1) % 3] - q * pb[(i + 2) % 3];
+        
+        if (!r) {
+            long long rev = pa[(i + 2) % 3];
+            if (0 > rev) {
+                rev += mod;
+            }
+            return rev;
+        }
+
+        a = b;
+        b = r;
+        i = (i + 1) % 3;
+    }
+}
+
+
+long long calc(long long m, long long n)
+{
+    const long long mod = 1000000007;
+    long long x;
+    long long total = 1;
+
+    long long d = n - m;
+    long long p = d < m ? d : m;
+    long long q = d < m ? m : d;
+
+    for (x = 2; x <= n; x++) {
+        total = (total * x) % mod;
+    }
+    for (x = 2; x <= p; x++) {
+        long long rev = mod_rev(x, mod);
+        total = (total * rev) % mod;
+        total = (total * rev) % mod;
+    }
+    for (; x <= q; x++) {
+        long long rev = mod_rev(x, mod);
+        total = (total * rev) % mod;
+    }
+    return total;
+}
diff --git a/old/pow_recr.c b/old/pow_recr.c
new file mode 100644
index 0000000..2ea8fd6
--- /dev/null
+++ b/old/pow_recr.c
@@ -0,0 +1,49 @@
+
+#include <stdio.h>
+
+float pow( float base, int exp )
+{
+  /**
+   * 该函数为 base != 0, exp >=1 编写
+   */
+
+  if ( exp == 1 ) {
+    return base;
+  } else {
+    return base * pow( base, exp - 1 );
+  }
+}
+
+
+int main()
+{
+  float a;
+  int b;
+
+  printf( "input a, b: " );
+  scanf( "%f %d", &a, &b );
+
+  /**
+   * 默认输入没有错误，且 b >= 0
+   */
+
+  if ( base == 0 ) {
+    if ( exp == 0 ) {
+      printf( "err to calc 0^0\n" );
+    } else {
+      printf( "0" );
+    }
+  } else {
+    if ( exp == 0 ) {
+      printf( "1" );
+    } else if ( exp > 0 ) {
+      printf( "%f", exp( a, b ) );
+    } else {
+      printf( "%f", 1 / exp( a, 0 - b ) );
+    }
+  }
+
+  printf( "\n" );
+  return 0;
+}
+
diff --git a/old/recurring_decimal_digit.c b/old/recurring_decimal_digit.c
new file mode 100644
index 0000000..9e1e67a
--- /dev/null
+++ b/old/recurring_decimal_digit.c
@@ -0,0 +1,96 @@
+#include <stdio.h>
+
+typedef unsigned long long int ul;
+
+
+ul gcd(ul a, ul b)
+{
+    if (!b) return a;
+    return gcd(b, a % b);
+}
+
+
+char recurring_decimal_digit(ul a, ul b, ul n)
+{
+    ul d = gcd(a, b);
+    a /= d;
+    b /= d;
+
+    /* 将
+     * \frac{a}{b}
+     * 转化为
+     * \frac{a}{2^{b2} \cdot 5^{b5} \cdot b'}
+     * 的形式
+     */
+    ul b2 = 0;
+    ul b5 = 0;
+    for (; !(b % 2); b /= 2) b2 += 1;
+    for (; !(b % 5); b /= 5) b5 += 1;
+
+    /* 计算
+     * \frac{1}{10^\mbox{offset}} \cdot \frac{a \cdot m}{b}
+     * 其中
+     * \mbox{offset} = \max(c2, c5)
+     * m = \frac{10^\mbox{offset}}{2^{b2} \cdot 5^{b5}}
+     * 
+     * offset 表示原小数中前 offset 位不在循环体内
+     */
+    ul m = 1;
+    ul base = 2;
+    ul offset = b5;
+    ul exp = b5 - b2;
+    if (b2 > b5) {
+        base = 5;
+        offset = b2;
+        exp = b2 - b5;
+    }
+    while (exp--) m *= base;
+
+    /*
+     * 计算
+     * \frac{1}{10^\mbox{offset}} \cdot \left( \mbox{pre} + \frac{r_m \cdot r_a \mod b}{b} \right)
+     * 其中
+     * \frac{r_m \cdot r_a \mod b}{b}
+     * 为纯循环小数，容易计算循环节
+     */
+    ul qm = m / b;
+    ul rm = m % b;
+    ul qa = a / b;
+    ul ra = a % b;
+    ul pre = (qa * b + ra) * qm + qa * rm;
+
+    /* 若 n 在非循环节中，则直接返回 pre 中对应的数位 */
+    if (n <= offset) {
+        n = offset - n;
+        while (n--) pre /= 10;
+        return pre % 10;
+    }
+
+    n -= offset;
+    a = rm * ra % b;
+    if (!a) return 0;   // 有限小数补0
+
+    /* 计算循环节unit，进而将 n 轮运算优化为 n % unit 轮 */
+    ul unit = 1;
+    ul mod = 10;
+    for (; 1 != mod; mod = (10 * mod) % b) unit += 1;
+
+    ul r = 0;
+    n %= unit;
+    if (!n) n = unit;
+    while (n--) {
+        a *= 10;
+        r = a / b;
+        a -= r * b;
+    }
+
+    return r % 10;
+}
+
+
+int main(int argc, char **argv)
+{
+    if (3 > argc) return -1;
+    printf("%d\n", recurring_decimal_digit(atoi(argv[1]), atoi(argv[2]), atoi(argv[3])));
+    return 0;
+}
diff --git a/old/reverse_number.py b/old/reverse_number.py
new file mode 100644
index 0000000..3aa7c0b
--- /dev/null
+++ b/old/reverse_number.py
@@ -0,0 +1,39 @@
+
+def reverse_num_as_int(x):
+    if x < 0:
+        neg = True
+        x = -x
+    else:
+        neg = False
+        
+    while not (x % 10):
+        x //= 10
+    
+    rev = 0
+    while x:
+        rev *= 10
+        rev += x % 10
+        x //= 10
+    
+    if neg:
+        return -rev
+    else:
+        return rev
+
+
+import re
+    
+def reverse_num_as_str(s):
+    if s[0] == '-':
+        neg = True
+        s = s[1:]
+    else:
+        neg = False
+
+    s = re.sub(r'^0*', '', s)
+    s = re.sub(r'0*$', '', s)
+    
+    if neg:
+        return '-' + s[::-1]
+    else:
+        return s[::-1]
diff --git a/old/sort_prior_after.c b/old/sort_prior_after.c
new file mode 100644
index 0000000..f6bb0f0
--- /dev/null
+++ b/old/sort_prior_after.c
@@ -0,0 +1,80 @@
+#include <stdio.h>
+#include <string.h>
+
+int of_prior(char ch) { return ch >= 'a' && ch <= 'z'; };
+int of_after(char ch) { return ch >= 'A' && ch <= 'Z'; };
+
+
+char *find_end(int (*of)(char), char *s, char *e)
+{
+    char *p = s;
+    int l = e - s;
+    while (l && of(*p)) l--, p++;
+    if (l) return p;
+    return e;
+}
+
+
+void shift(char *s, char *e)
+{
+    e -= 1;
+    for (; s < e; s++, e--) {
+        char t = *e;
+        *e = *s;
+        *s = t;
+    }
+}
+
+
+int sort_cap(char *s, char *e)
+{
+    s = find_end(of_prior, s, e);
+    if (s == e) return -1;
+    for (;;) {
+        char *m = find_end(of_after, s, e);
+        if (m == e) return 0;
+        char *n = find_end(of_prior, m, e);
+        shift(s, m);
+        shift(m, n);
+        shift(s, n);
+        s += n - m;
+    }
+}
+
+
+void direct_method(char *s, char *e)
+{
+    char *cap = e;
+    char *p = e - 1;
+    for (; p >= s; p--) {
+        if (of_after(*p)) {
+            char *q = p;
+            for (; q < cap - 1; q++) {
+                char t = *q;
+                *q = q[1];
+                q[1] = t;
+            }
+            cap -= 1;
+        }
+    }
+}
+
+
+void dual_print(char *str, int len)
+{
+    int i;
+    for (i = 0; i < len; i++) if (of_prior(str[i])) putchar(str[i]);
+    for (i = 0; i < len; i++) if (of_after(str[i])) putchar(str[i]);
+    printf("\n");
+}
+
+
+int main()
+{
+    char buf[] = "AklBiCeilD";
+    //direct_method(buf, buf + strlen(buf));
+    sort_cap(buf, buf + strlen(buf));
+    printf("%s\n", buf);
+    //dual_print(buf, strlen(buf));
+    return 0;
+}
diff --git a/old/sqlist.c b/old/sqlist.c
new file mode 100644
index 0000000..9e2eea3
--- /dev/null
+++ b/old/sqlist.c
@@ -0,0 +1,171 @@
+#include <stdio.h>
+
+#define MAXSIZE 30
+
+struct _st_list {
+    int sqlist[MAXSIZE];
+    int size;
+};
+
+struct _st_list a = {{0, }, 0};
+
+
+static inline int *_get_head(struct _st_list *p)
+{
+    return p->sqlist;
+}
+
+static inline int *_get_tail(struct _st_list *p)
+{
+    return p->sqlist + p->size;
+}
+
+
+void show(struct _st_list *p)
+{
+    int *ptr = _get_head(p);
+    int *end = _get_tail(p);
+    printf("%d:\n", p->size);
+    for (; ptr < end; ptr++) {
+        printf("%d  ", *ptr);
+    }
+    printf("\n");
+}
+
+
+void insert(struct _st_list *p, int i, int x)
+{
+    if (p->size == MAXSIZE) return;
+    if (i < 0) return;
+    if (i > p->size) return;
+    int *ptr = _get_tail(p);
+    int *end = _get_head(p) + i;
+    for (; ptr > end; ptr--) {
+        *ptr = *(ptr - 1);
+    }
+    *ptr = x;
+    p->size += 1;
+}
+
+
+int delete(struct _st_list *p, int i)
+{
+    if (p->size == 0) return 0;
+    if (i < 0) return 0;
+    if (i >= p->size) return 0;
+    int *ptr = _get_head(p) + i;
+    int *end = _get_tail(p);
+    int del = *ptr;
+    for (; ptr < end; ptr++) {
+        *ptr = *(ptr + 1);
+    }
+    p->size -= 1;
+    return del;
+}
+
+
+static int _more_than(int a, int b) { return a > b; }
+static int _less_than(int a, int b) { return a < b; }
+
+static int _trace_pick(struct _st_list *p, int (*match)(int, int))
+{
+    if (!p->size) return 0;
+    int *ptr = _get_head(p);
+    int *end = _get_tail(p);
+    int fetch = *ptr++;
+    for (; ptr < end; ptr++) {
+        if (match(*ptr, fetch)) fetch = *ptr;
+    }
+    return fetch;
+}
+
+
+int min(struct _st_list *p)
+{
+    return _trace_pick(p, _less_than);
+}
+
+
+int max(struct _st_list *p)
+{
+    return _trace_pick(p, _more_than);
+}
+
+
+static int *_iter_bisearch(int *s, int *e, int x)
+{
+    if (e - s < 2) {
+        if (x > *s) return e;
+        else        return s;
+    }
+    int *m = s + (e - s) / 2;
+    if (x > *m) return _iter_bisearch(m, e, x);
+    else        return _iter_bisearch(s, m, x);
+}
+
+
+static int _bisearch(struct _st_list *p, int x)
+{
+    int *ptr = _get_head(p);
+    int *end = _get_tail(p);
+    return _iter_bisearch(ptr, end, x) - _get_head(p);
+}
+
+
+void biinsert(struct _st_list *p, int x)
+{
+    insert(p, _bisearch(p, x), x);
+}
+
+
+static void _iter_sort(int *s, int *e)
+{
+    if (e <= s) return;
+
+    int v = *s;
+    int *p = s;
+    int *q = e;
+    for (;;) {
+        while ((p < q) && (*q >= v)) q -= 1;
+        *p++ = *q;
+        if (p >= q) {
+            p = q;
+            break;
+        }
+        while ((p < q) && (*p <= v)) p += 1;
+        *q-- = *p;
+        if (p >= q) break;
+    }
+    *p = v;
+
+    _iter_sort(s, p - 1);
+    _iter_sort(p + 1, e);
+}
+
+
+void sort(struct _st_list *p)
+{
+    if (p->size < 2) return;
+    _iter_sort(_get_head(p), _get_tail(p) - 1);
+}
+
+
+int main()
+{
+    printf("========= start ==========\n");
+    insert(&a, 0, 7);
+    insert(&a, 0, 6);
+    insert(&a, 0, 3);
+    insert(&a, 0, 9);
+    insert(&a, 0, 1);
+    insert(&a, 0, 4);
+    insert(&a, 0, 2);
+    insert(&a, 0, 8);
+    show(&a);
+    sort(&a);
+    show(&a);
+    biinsert(&a, 5);
+    show(&a);
+    printf("########## end ##########\n");
+    return 0;
+}
diff --git a/old/stamp_crop.c b/old/stamp_crop.c
new file mode 100644
index 0000000..abfe5d9
--- /dev/null
+++ b/old/stamp_crop.c
@@ -0,0 +1,100 @@
+#include <stdio.h>
+#include <unistd.h>
+#include <stdbool.h>
+
+#define NUM_TOTAL   12
+#define NUM_COLUMN  4
+#define NUM_CROP    5
+
+typedef struct {
+  char crop[ NUM_CROP ];
+  char flag[ NUM_CROP ];
+} st;
+
+
+void chk( char *buf, int len )
+{
+  for ( int i = 0; i < len; i++ ) {
+    printf( "%d ", *buf++ );
+  }
+  printf( "\n" );
+}
+
+
+bool next( st *g )
+{
+  for ( int i = NUM_CROP - 1; i >= 0; i-- )
+    if ( NUM_TOTAL - NUM_CROP > g->crop[ i ] - i ) {
+      g->crop[ i++ ] += 1;
+
+      for ( ; i < NUM_CROP; i++ )
+        g->crop[ i ] = g->crop[ i - 1 ] + 1;
+
+      return true;
+    }
+
+  return false;
+}
+
+
+char flag_set( st *g, int index, char target_flag )
+{
+  char cur_flag = g->flag[ index ];
+  g->flag[ index ] = target_flag;
+  if ( cur_flag )
+    for ( int i = 0; i < index; i++ )
+      if ( g->flag[ i ] == cur_flag )
+        g->flag[ i ] = target_flag;
+  return 1;
+}
+
+
+bool continuity( st *g )
+{
+  char base_flag = 1;
+  memset( g->flag, 0, NUM_CROP );
+
+  for ( int j = 0; j < NUM_CROP; j++ ) {
+    char connected = 0;
+
+    for ( int i = 0; i < j; i++ ) {
+      switch ( g->crop[ j ] - g->crop[ i ] ) {
+
+        case NUM_COLUMN:
+          connected += flag_set( g, j, g->flag[ i ] );
+          break;
+
+        case 1:
+          if ( g->crop[ j ] % NUM_COLUMN )
+            connected += flag_set( g, j, g->flag[ i ] );
+          break;
+      }
+    }
+
+    if ( ! connected ) g->flag[ j ] = base_flag++;
+  }
+
+  char cur_flag = g->flag[ 0 ];
+  for ( int i = 1; i < NUM_CROP; i++ )
+    if ( g->flag[ i ] != cur_flag )
+      return false;
+
+  return true;
+}
+
+
+int main()
+{
+  st g;
+  for ( int i = 0; i < NUM_CROP; i++ ) {
+    g.crop[ i ] = i;
+  }
+
+  int count = 0;
+  do {
+    if ( continuity( &g ) ) count += 1;
+  } while ( next( &g ) );
+
+  printf( "%d\n", count );
+  return 0;
+}