数据结构-＞9.1顺序查找和二分查找

1.代码实现

代码如下（示例）：

#include <stdio.h>
#include <malloc.h>

typedef struct Node {
	int key;
	char value;
}Node, * NodePtr;

typedef struct SequentialList {
	int lenth;
	NodePtr elements;
}SequentialList, * ListPtr;

ListPtr initList(int* paraKeys, char* paraValues, int paralenth) {
	int i;
	ListPtr resultPtr = (ListPtr)malloc(sizeof(SequentialList));
	resultPtr->lenth = paralenth;
	resultPtr->elements = (NodePtr)malloc((paralenth + 1) * sizeof(Node));
	for (int i = 0; i < paralenth; i++) {
		resultPtr->elements[i].key = paraKeys[i];
		resultPtr->elements[i].value = paraValues[i];
	}

	return resultPtr;
}

char sequentialSearch(ListPtr paraListPtr, int paraKey) {
	int i=0;
	paraListPtr->elements[paraListPtr->lenth].key = paraKey;
	paraListPtr->elements[paraListPtr->lenth].value = 'x';

	while (paraListPtr->elements[i].key != paraKey) {
		i++;
	}

	return paraListPtr->elements[i].value;
}

void sequentialSearchTest() {
	int tempUnsortedKeys[] = { 4, 5, 3, 6, 10, 7, 1, 9 };
	char tempContents[] = { 'h', 'e', 'l', 'o', 'w', 'r', 'd', '!' };
	ListPtr tempListPtr = initList(tempUnsortedKeys, tempContents, 8);

	printf("Search result of 10 is: %c\r\n", sequentialSearch(tempListPtr, 10));
	printf("Search result of 5 is: %c\r\n", sequentialSearch(tempListPtr, 5));
	printf("Search result of 4 is: %c\r\n", sequentialSearch(tempListPtr, 4));
	printf("Search result of 2 is: %c\r\n", sequentialSearch(tempListPtr, 2));
}

char binarySearch(ListPtr paraListPtr, int paraKey) {
	int tempLeft = 1;
	int tempRight = paraListPtr->lenth;
	int tempMiddle = (tempLeft + tempRight) / 2;

	while (tempLeft <= tempRight) {
		tempMiddle = (tempLeft + tempRight) / 2;
		if (paraListPtr->elements[tempMiddle].key == paraKey) {
			return paraListPtr->elements[tempMiddle].value;
		}
		else if (paraListPtr->elements[tempMiddle].key < paraKey) {
			tempLeft = tempMiddle + 1;
		}
		else {
			tempRight = tempMiddle - 1;
		}
	}

	return 'x';
}

void binarySearchTest() {
	int tempUnsortedKeys[] = { 1, 3, 4, 5, 6, 7, 9, 10 };
	char tempContents[] = { 'h', 'e', 'l', 'o', 'w', 'r', 'd', '!' };
	ListPtr tempListPtr = initList(tempUnsortedKeys, tempContents, 8);

	printf("Search result of 10 is: %c\r\n", binarySearch(tempListPtr, 10));
	printf("Search result of 5 is: %c\r\n", binarySearch(tempListPtr, 5));
	printf("Search result of 4 is: %c\r\n", binarySearch(tempListPtr, 4));
	printf("Search result of 2 is: %c\r\n", binarySearch(tempListPtr, 2));
}

int main() {
	printf("\r\n------sequentialSearchTest------\r\n");
	sequentialSearchTest();

	printf("\r\n------binarySearchTest------\r\n");
	binarySearchTest();
	return 1;
}

2.读入数据

代码如下（示例）：

------sequentialSearchTest------
Search result of 10 is: w
Search result of 5 is: e
Search result of 4 is: h
Search result of 2 is: x

------binarySearchTest------
Search result of 10 is: !
Search result of 5 is: o
Search result of 4 is: l
Search result of 2 is: x

---

# 总结
顺序查找：
1.点睛之笔：多开辟一个空间，赋值-1，‘x’，所以无论表中是否存在需要查询的元素，结果总是不会越界。
2.所以这个节点可以加在开头，也可以加在结尾，此代码为在结尾添加了一个哨兵。
二分查找：
设立左右“指针”，每次取中间值来查询key，如果中间值比key大，就右“指针”=middle-1;否则相反为左“指针”=middle+1;直到查询到指定元素或者哨兵。