diff --git a/【实践课外】9.数组3/7-1 删除重复字符.c b/【实践课外】9.数组3/7-1 删除重复字符.c
new file mode 100644
index 0000000..be2347f
--- /dev/null
+++ b/【实践课外】9.数组3/7-1 删除重复字符.c	
@@ -0,0 +1,25 @@
+#include <stdio.h>
+#include <string.h>
+
+int cnt[256];
+char s[100];
+
+int main() {
+    gets(s);
+
+    int len = strlen(s);
+
+    for (int i = 0; i < len; i++) {
+        cnt[s[i]]++;
+    }
+
+    for (char i = 32; i <= 126; i++) {
+        if (cnt[i] > 0) {
+            printf("%c", i);
+        }
+    }
+
+    printf("\n");
+
+    return 0;
+}
diff --git a/【实践课外】9.数组3/7-1 删除重复字符.png b/【实践课外】9.数组3/7-1 删除重复字符.png
new file mode 100644
index 0000000..839efd6
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diff --git a/【实践课外】9.数组3/7-2 说反话-加强版.c b/【实践课外】9.数组3/7-2 说反话-加强版.c
new file mode 100644
index 0000000..4c16e02
--- /dev/null
+++ b/【实践课外】9.数组3/7-2 说反话-加强版.c	
@@ -0,0 +1,43 @@
+#include <stdio.h>
+#include <string.h>
+
+char s[500005];
+int cnt, start_pos[500005], len[500005];
+
+int main() {
+    gets(s);
+
+    int len_s = strlen(s);
+
+    for (int i = 0; i < len_s; i++) {
+        if (s[i] == ' ') {
+            if (i == 0 || s[i - 1] == ' ') {
+                continue;
+            }
+            start_pos[cnt] = i - len[cnt];
+            cnt++;
+            len[cnt] = 0;
+        } else {
+            len[cnt]++;
+        }
+    }
+
+    if (len_s > 0 && s[len_s - 1] != ' ') {
+        start_pos[cnt] = len_s - len[cnt];
+        cnt++;
+    }
+
+    for (int i = cnt - 1; i >= 0; i--) {
+        for (int j = start_pos[i]; j < start_pos[i] + len[i]; j++) {
+            printf("%c", s[j]);
+        }
+
+        if (i != 0) {
+            printf(" ");
+        } else {
+            printf("\n");
+        }
+    }
+
+    return 0;
+}
diff --git a/【实践课外】9.数组3/7-2 说反话-加强版.png b/【实践课外】9.数组3/7-2 说反话-加强版.png
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index 0000000..4441eb1
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diff --git a/【实践课外】9.数组3/7-3 数组-回文串.c b/【实践课外】9.数组3/7-3 数组-回文串.c
new file mode 100644
index 0000000..9b384af
--- /dev/null
+++ b/【实践课外】9.数组3/7-3 数组-回文串.c	
@@ -0,0 +1,31 @@
+#include <stdio.h>
+#include <string.h>
+
+int n;
+char s[1005];
+
+int main() {
+    int n;
+
+    scanf("%d", &n);
+
+    for (int i = 1; i <= n; i++) {
+        scanf("%s", s);
+
+        int flag = 1;
+
+        // check is palindrome
+        for (int j = 0; j < strlen(s) / 2; j++) {
+            if (s[j] != s[strlen(s) - j - 1]) {
+                flag = 0;
+                break;
+            }
+        }
+
+        if (flag) {
+            printf("%s\n", s);
+        }
+    }
+
+    return 0;
+}
diff --git a/【实践课外】9.数组3/7-3 数组-回文串.png b/【实践课外】9.数组3/7-3 数组-回文串.png
new file mode 100644
index 0000000..f56c233
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diff --git a/【实践课外】9.数组3/7-4 数组-无聊的菇菇一族.c b/【实践课外】9.数组3/7-4 数组-无聊的菇菇一族.c
new file mode 100644
index 0000000..c115e0e
--- /dev/null
+++ b/【实践课外】9.数组3/7-4 数组-无聊的菇菇一族.c	
@@ -0,0 +1,23 @@
+#include <stdio.h>
+#include <string.h>
+
+int n;
+char s[105];
+
+int main() {
+    scanf("%d", &n);
+
+    for (int i = 1; i <= n; i++) {
+        scanf("%s", s);
+
+        int len = strlen(s);
+
+        for (int j = len - 1; j >= 0; j--) {
+            printf("%c", s[j]);
+        }
+
+        printf("\n");
+    }
+
+    return 0;
+}
diff --git a/【实践课外】9.数组3/7-4 数组-无聊的菇菇一族.png b/【实践课外】9.数组3/7-4 数组-无聊的菇菇一族.png
new file mode 100644
index 0000000..920c58d
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diff --git a/【实践课外】9.数组3/7-5 数组-文本加密.c b/【实践课外】9.数组3/7-5 数组-文本加密.c
new file mode 100644
index 0000000..e7b025b
--- /dev/null
+++ b/【实践课外】9.数组3/7-5 数组-文本加密.c	
@@ -0,0 +1,47 @@
+#include <stdio.h>
+#include <string.h>
+
+char s[2][10005];
+int len0, len1;
+
+int main() {
+    while (s[0][len0] = getchar(), s[0][len0] != ',') {
+        len0++;
+    }
+
+    s[0][len0] = '\0';
+
+    while ((s[1][len1] = getchar()) != EOF && s[1][len1] != '\n') {
+        len1++;
+    }
+
+    s[1][len1] = '\0';
+
+    for (int i = 0; s[0][i] != '\0'; i++) {
+        if ('A' <= s[0][i] && s[0][i] <= 'Z') {
+            s[0][i] = 'a' + s[0][i] - 'A';
+
+            s[0][i] -= 2;
+
+            if (s[0][i] < 'a') {
+                s[0][i] += 26;
+            }
+        } else if ('a' <= s[0][i] && s[0][i] <= 'z') {
+            s[0][i] = 'A' + s[0][i] - 'a';
+
+            s[0][i] -= 2;
+
+            if (s[0][i] < 'A') {
+                s[0][i] += 26;
+            }
+        }
+    }
+
+    if (strcmp(s[0], s[1]) == 0) {
+        printf("Yes\n");
+    } else {
+        printf("No\n");
+    }
+
+    return 0;
+}
diff --git a/【实践课外】9.数组3/7-5 数组-文本加密.png b/【实践课外】9.数组3/7-5 数组-文本加密.png
new file mode 100644
index 0000000..a7889f3
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diff --git a/【实践课外】9.数组3/7-6 数组-动车上.c b/【实践课外】9.数组3/7-6 数组-动车上.c
new file mode 100644
index 0000000..0a73e5a
--- /dev/null
+++ b/【实践课外】9.数组3/7-6 数组-动车上.c	
@@ -0,0 +1,33 @@
+#include <stdio.h>
+#include <string.h>
+
+int k;
+char s[105];
+
+int main() {
+    scanf("%d\n%s", &k, s);
+
+    int len = strlen(s);
+
+    for (int i = 0, cnt = 0; i < len; i += k, cnt++) {
+        if (i + k - 1 < len) {
+            if (cnt % 2 == 1) {
+                for (int j = i + k - 1; j >= i; j--) {
+                    printf("%c", s[j]);
+                }
+            } else {
+                for (int j = i; j < i + k; j++) {
+                    printf("%c", s[j]);
+                }
+            }
+        } else {
+            for (int j = i; j < len; j++) {
+                printf("%c", s[j]);
+            }
+        }
+    }
+
+    printf("\n");
+
+    return 0;
+}
diff --git a/【实践课外】9.数组3/7-6 数组-动车上.png b/【实践课外】9.数组3/7-6 数组-动车上.png
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index 0000000..90d75a8
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