【机试练习】【C++】二分

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# include<cstdio>

using namespace std;

int sampleArray[7] = {1, 2, 3, 3, 3, 5, 6};

int binarySearch(int sa[], int target, int left, int right){
	int mid = - 1;
	while(left <= right){
		mid = left + (right - left) / 2; // 防止int越界溢出 
		if(sa[mid] == target) return mid;
		else if(sa[mid] > target) right = mid - 1;
		else left = mid + 1;
	}
	return -1;
}

// 以下两个是查找符合条件区间[L, R)的函数 
int binarySearchL(int sa[], int target, int left, int right){
	int mid = -1;
	while(left < right){ // 这里要修改了 
		mid = left + (right - left) / 2;
		if(sa[mid] >= target) right = mid; //符合大于等于这个条件，就往左半区间查找 
		//else if(sa[mid] > target) right = mid - 1; 这样写是错的 
		else left = mid + 1; // 不符合条件，就往右半区间查找 
	} 
	return left; // 最后left == right ,随便return一个 
}

int binarySearchR(int sa[], int target, int left, int right){
	int mid = -1;
	while(left < right){
		mid = left + (right - left) / 2;
		if(sa[mid] > target) right = mid;
		else left = mid + 1; 
	}
	return left;
}


int main(){
	printf("数组成员为:\n");
	int T = 7;
	for(int i = 0; i < T; i++){
		printf("%d ", sampleArray[i]);
	}
	printf("\n");
	printf("尝试查找3，返回：%d\n",binarySearch(sampleArray, 3, 0, 6));
	printf("尝试查找5，返回：%d\n",binarySearch(sampleArray, 5, 0, 6));
	printf("尝试查找11，返回：%d\n",binarySearch(sampleArray, 11, 0, 6));
	
	printf("尝试查找3的区间，返回：[%d, %d)\n",binarySearchL(sampleArray, 3, 0, 6)
											,binarySearchR(sampleArray, 3, 0, 6));
	printf("尝试查找5的区间，返回：[%d, %d)\n",binarySearchL(sampleArray, 5, 0, 6)
											,binarySearchR(sampleArray, 5, 0, 6));
	// L == R 时， 要查找的数字不存在 
	printf("尝试查找13的区间，返回：[%d, %d)\n",binarySearchL(sampleArray, 13, 0, 6)
											,binarySearchR(sampleArray, 13, 0, 6));
	
	return 0;
}