Simplify struct declarations of C.

Use PascalCase for all structs in C.
SImplify n_queens.c
Format C code for chapter of graph.

codes/c/chapter_searching/two_sum.c

@@ -23,26 +23,24 @@ int *twoSumBruteForce(int *nums, int numsSize, int target, int *returnSize) {
 }
 
 /* 哈希表 */
-struct hashTable {
+typedef struct {
     int key;
     int val;
     UT_hash_handle hh; // 基于 uthash.h 实现
-};
-
-typedef struct hashTable hashTable;
+} HashTable;
 
 /* 哈希表查询 */
-hashTable *find(hashTable *h, int key) {
-    hashTable *tmp;
+HashTable *find(HashTable *h, int key) {
+    HashTable *tmp;
     HASH_FIND_INT(h, &key, tmp);
     return tmp;
 }
 
 /* 哈希表元素插入 */
-void insert(hashTable *h, int key, int val) {
-    hashTable *t = find(h, key);
+void insert(HashTable *h, int key, int val) {
+    HashTable *t = find(h, key);
     if (t == NULL) {
-        hashTable *tmp = malloc(sizeof(hashTable));
+        HashTable *tmp = malloc(sizeof(HashTable));
         tmp->key = key, tmp->val = val;
         HASH_ADD_INT(h, key, tmp);
     } else {
@@ -52,9 +50,9 @@ void insert(hashTable *h, int key, int val) {
 
 /* 方法二：辅助哈希表 */
 int *twoSumHashTable(int *nums, int numsSize, int target, int *returnSize) {
-    hashTable *hashtable = NULL;
+    HashTable *hashtable = NULL;
     for (int i = 0; i < numsSize; i++) {
-        hashTable *t = find(hashtable, target - nums[i]);
+        HashTable *t = find(hashtable, target - nums[i]);
         if (t != NULL) {
             int *res = malloc(sizeof(int) * 2);
             res[0] = t->val, res[1] = i;