Refactor the articles related to searching algorithm. Add the chapter of binary search. Add the section of searching algorithm revisited. (#464)

codes/c/chapter_searching/CMakeLists.txt

@@ -1,3 +1,2 @@
-add_executable(binary_search binary_search.c )
-add_executable(linear_search linear_search.c)
-add_executable(hashing_search hashing_search.c)
+add_executable(binary_search binary_search.c)
+add_executable(leetcode_two_sum leetcode_two_sum.c)

codes/c/chapter_searching/binary_search.c

@@ -1,59 +0,0 @@
-/**
- * File: binary_search.c
- * Created Time: 2023-03-18
- * Author: Guanngxu (446678850@qq.com)
- */
-
-#include "../include/include.h"
-
-/* 二分查找（双闭区间） */
-int binarySearch(int *nums, int len, int target) {
-    // 初始化双闭区间 [0, n-1] ，即 left, right 分别指向数组首元素、尾元素
-    int left = 0, right = len - 1;
-    // 循环，当搜索区间为空时跳出（当 left > right 时为空）
-    while (left <= right) {
-        int mid = (left + right) / 2; // 计算中点索引 mid
-        if (nums[mid] < target)       // 此情况说明 target 在区间 [mid+1, right] 中
-            left = mid + 1;
-        else if (nums[mid] > target)  // 此情况说明 target 在区间 [left, mid-1] 中
-            right = mid - 1;
-        else                          // 找到目标元素，返回其索引
-            return mid;
-    }
-    // 未找到目标元素，返回 -1
-    return -1;
-}
-
-/* 二分查找（左闭右开） */
-int binarySearch1(int *nums, int len, int target) {
-    // 初始化左闭右开 [0, n) ，即 left, right 分别指向数组首元素、尾元素+1
-    int left = 0, right = len;
-    // 循环，当搜索区间为空时跳出（当 left = right 时为空）
-    while (left < right) {
-        int mid = (left + right) / 2; // 计算中点索引 mid
-        if (nums[mid] < target)       // 此情况说明 target 在区间 [mid+1, right) 中
-            left = mid + 1;
-        else if (nums[mid] > target)  // 此情况说明 target 在区间 [left, mid) 中
-            right = mid;
-        else                          // 找到目标元素，返回其索引
-            return mid;
-    }
-    // 未找到目标元素，返回 -1
-    return -1;
-}
-
-/* Driver Code */
-int main() {
-    int target = 6;
-    int nums[10] = { 1, 3, 6, 8, 12, 15, 23, 67, 70, 92 };
-    
-    /* 二分查找（双闭区间） */
-    int index = binarySearch(nums, 10, target);
-    printf("目标元素 6 的索引 = %d\n", index);
-
-    /* 二分查找（左闭右开） */
-    index = binarySearch1(nums, 10, target);
-    printf("目标元素 6 的索引 = %d\n", index);
-    
-    return 0;
-}

codes/c/chapter_searching/leetcode_two_sum.c

@@ -0,0 +1,85 @@
+/**
+ * File: leetcode_two_sum.c
+ * Created Time: 2023-01-19
+ * Author: Reanon (793584285@qq.com)
+ */
+
+#include "../include/include.h"
+
+/* 方法一：暴力枚举 */
+int *twoSumBruteForce(int *nums, int numsSize, int target, int *returnSize) {
+    for (int i = 0; i < numsSize; ++i) {
+        for (int j = i + 1; j < numsSize; ++j) {
+            if (nums[i] + nums[j] == target) {
+                int *ret = malloc(sizeof(int) * 2);
+                ret[0] = i, ret[1] = j;
+                *returnSize = 2;
+                return ret;
+            }
+        }
+    }
+    *returnSize = 0;
+    return NULL;
+}
+
+/* 哈希表 */
+struct hashTable {
+    int key;
+    int val;
+    // 借助 LetCode 上常用的哈希表
+    UT_hash_handle hh;
+};
+
+typedef struct hashTable hashTable;
+
+hashTable *find(hashTable *h, int key) {
+    hashTable *tmp;
+    HASH_FIND_INT(h, &key, tmp);
+    return tmp;
+}
+
+void insert(hashTable *h, int key, int val) {
+    hashTable *t = find(h, key);
+    if (t == NULL) {
+        hashTable *tmp = malloc(sizeof(hashTable));
+        tmp->key = key, tmp->val = val;
+        HASH_ADD_INT(h, key, tmp);
+    } else {
+        t->val = val;
+    }
+}
+
+/* 方法二：辅助哈希表 */
+int *twoSumHashTable(int *nums, int numsSize, int target, int *returnSize) {
+    hashTable *hashtable = NULL;
+    for (int i = 0; i < numsSize; i++) {
+        hashTable *t = find(hashtable, target - nums[i]);
+        if (t != NULL) {
+            int *ret = malloc(sizeof(int) * 2);
+            ret[0] = t->val, ret[1] = i;
+            *returnSize = 2;
+            return ret;
+        }
+        insert(hashtable, nums[i], i);
+    }
+    *returnSize = 0;
+    return NULL;
+}
+
+int main() {
+    // ======= Test Case =======
+    int nums[] = {2, 7, 11, 15};
+    int target = 9;
+    // ====== Driver Code ======
+    int returnSize;
+    int *res = twoSumBruteForce(nums, sizeof(nums) / sizeof(int), target, &returnSize);
+    // 方法一
+    printf("方法一 res = ");
+    printArray(res, returnSize);
+
+    // 方法二
+    res = twoSumHashTable(nums, sizeof(nums) / sizeof(int), target, &returnSize);
+    printf("方法二 res = ");
+    printArray(res, returnSize);
+    return 0;
+}