From b4ebda4fc94e4505ff268ec0e08bd951911e26c5 Mon Sep 17 00:00:00 2001
From: C_W <chaow2024@gmail.com>
Date: Tue, 10 Dec 2024 16:52:12 +1100
Subject: [PATCH] =?UTF-8?q?=E6=B7=BB=E5=8A=A00028=E5=AE=9E=E7=8E=B0strStr?=
 =?UTF-8?q?=20C=20=E7=89=88=E6=9C=AC?=
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---
 problems/0028.实现strStr.md | 64 +++++++++++++++++++++++++++++++++++
 1 file changed, 64 insertions(+)

diff --git a/problems/0028.实现strStr.md b/problems/0028.实现strStr.md
index e0cb123e..63a08d96 100644
--- a/problems/0028.实现strStr.md
+++ b/problems/0028.实现strStr.md
@@ -1456,6 +1456,70 @@ public int[] GetNext(string needle)
 }
 ```
 
+### C:
+
+> 前缀表统一右移和减一
+
+```c
+
+int *build_next(char* needle, int len) {
+
+    int *next = (int *)malloc(len * sizeof(int));
+    assert(next); // 确保分配成功
+
+    // 初始化next数组
+    next[0] = -1; // next[0] 设置为 -1，表示没有有效前缀匹配
+    if (len <= 1) { // 如果模式串长度小于等于 1，直接返回
+        return next;
+    }
+    next[1] = 0; // next[1] 设置为 0，表示第一个字符没有公共前后缀
+
+    // 构建next数组， i 从模式串的第三个字符开始， j 指向当前匹配的最长前缀长度
+    int i = 2, j = 0;
+    while (i < len) {
+        if (needle[i - 1] == needle[j]) {
+            j++;
+            next[i] = j;
+            i++;
+        } else if (j > 0) {
+            // 如果不匹配且 j > 0， 回退到次长匹配前缀的长度
+            j = next[j];
+        } else {
+            next[i] = 0;
+            i++;
+        }
+    }
+    return next;
+}
+
+int strStr(char* haystack, char* needle) {
+
+    int needle_len = strlen(needle);
+    int haystack_len = strlen(haystack);
+
+    int *next = build_next(needle, needle_len);
+
+    int i = 0, j = 0; // i 指向主串的当前起始位置, j 指向模式串的当前匹配位置
+    while (i <= haystack_len - needle_len) {
+        if (haystack[i + j] == needle[j]) {
+            j++;
+            if (j == needle_len) {
+                free(next);
+                next = NULL
+                return i;
+            }
+        } else {
+            i += j - next[j]; // 调整主串的起始位置
+            j = j > 0 ? next[j] : 0;
+        }
+    }
+
+    free(next);
+    next = NULL;
+    return -1;
+}
+```
+
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