diff --git a/CSP-Training/5/2-string.cpp b/CSP-Training/5/2-string.cpp
new file mode 100644
index 0000000..ad35f4b
--- /dev/null
+++ b/CSP-Training/5/2-string.cpp
@@ -0,0 +1,40 @@
+//01串
+#include <cstdio>
+#include <iostream>
+using namespace std;
+
+int main()
+{
+    int n;
+    int num[100], sum, maxsum = 0, oneCount = 0;
+    scanf("%d", &n);
+    for (int i = 0; i < n; i++)
+    {
+        scanf("%d", &num[i]);
+    }
+    for (int i = 0; i < n; i++) //枚举左端点
+    {
+        for (int j = i; j < n; j++) //枚举右端点
+        {
+            sum = 0;
+            for (int k = 0; k < i; k++) //之前
+            {
+                sum += num[k];
+            }
+            for (int k = i; k <= j; k++) //中间
+            {
+                sum += 1 - num[k];
+            }
+            for (int k = j + 1; k < n; k++) //之后
+            {
+                sum += num[k];
+            }
+            if (sum > maxsum)
+            {
+                maxsum = sum;
+            }
+        }
+    }
+    printf("%d", maxsum);
+    return 0;
+}
\ No newline at end of file