查找与排序-KMP算法

C++常用的排序算法：

冒泡排序

void BubbleSort(int *a,int len)
{
    int temp;
    for(int i=0; i<len; ++i){
        for(int j=0; j<len-i-1; ++j){
            if(a[j]>a[j+1]){
                temp =a[j];
                a[j] = a[j+1];
                a[j+1] = temp;
            }
        }
    }

选择排序

void SelectSort(int *a,int len)
{
    for(int i=0; i<len; ++i){
        int m_index = i;
        for(int j=i+1; j<len; ++j){
            if(a[j] < a[m_index]){
                m_index = j;
            }
        }
        int temp = a[m_index];
        a[m_index] = a[i];
        a[i] = temp;
    }

插入排序

void InsertSort(int *a,int len)
{
    for(int i=0; i<len; ++i){
        for(int j=i; j>0; --j){
            if(a[j]<a[j-1]){
                int temp = a[j];
                a[j] = a[j-1];
                a[j-1] = temp;
            }
        }
    }

希尔排序

int shell_sort(int *data, int length) {

	int gap = 0;
	int i = 0, j = 0;
	int temp;

	for (gap = length / 2;gap >= 1; gap /= 2) {  //分组

		for (i = gap;i < length;i ++) {

			temp = data[i];
			for (j = i-gap;j >= 0 && temp < data[j];j = j - gap) {

				data[j+gap] = data[j];
				
			}
			data[j+gap] = temp;
		}

	}

	return 0;
}

归并排序

void merge(int *data, int *temp, int start, int middle, int end) { //后合并

	int i = start, j = middle+1, k = start;

	while (i <= middle && j <= end) {
		if (data[i] > data[j]) {
			temp[k++] = data[j++];
		} else {
			temp[k++] = data[i++];
		}
	}

	while (i <= middle) {
		temp[k++] = data[i++];
	}

	while (j <= end) {
		temp[k++] = data[j++];
	}

	for (i = start;i <= end;i ++) {
		data[i] = temp[i];
	}
}


int merge_sort(int *data, int *temp, int start, int end) {  //先分

	int middle;
	
	if (start < end) {
		middle = start + (end - start) / 2;

		merge_sort(data, temp, start, middle);
		merge_sort(data, temp, middle+1, end);

		merge(data, temp, start, middle, end);
	}

} 

快排

void sort(int *data, int left, int right) {

	if (left >= right) return ;

	int i = left;
	int j = right;
	int key = data[left];

	while (i < j) {

		while (i < j && key <= data[j]) {
			j --;
		}
		data[i] = data[j];

		while (i < j && key >= data[i]) {
			i ++;
		}
		data[j] = data[i];
	}

	data[i] = key;

	sort(data, left, i - 1);
	sort(data, i + 1, right);
}

在一个字符串中，查找匹配子串，常用的KMP算法

void make_next(const char *pattern, int *next) {

	int q, k;
	int m = strlen(pattern);

	next[0] = 0;
	for (q = 1,k = 0;q < m; q ++) {

		while (k > 0 && pattern[q] != pattern[k])
			k = next[k-1];

		if (pattern[q] == pattern[k]) {
			k ++;
		}

		next[q] = k;

	}
     // 假设 pattern = "abcabd"
	// next[0] = 0;
	// q=1, k=0, pattern[q]:pattern[k] = b:a, next[1] = 0;
	// q=2, k=0, pattern[q]:pattern[k] = c:a, next[2] = 0;
	// q=3, k=0, pattern[q]:pattern[k] = a:a, k++, next[3] = 1;
	// q=4, k=1, pattern[q]:pattern[k] = b:b, k++, next[4] = 2;
	// q=5, k=2, pattern[q]:pattern[k] = c:c, k++, next[5] = 3;
	// q=6, k=3, pattern[q]:pattern[k] = d:a, k=next[k-1] -> k=0; next[6] = 0;

}


int kmp(const char *text, const char *pattern, int *next) {

	int n = strlen(text);
	int m = strlen(pattern);

	make_next(pattern, next);
	
	int i, q;
	for (i = 0, q = 0;i < n;i ++) {

		while (q > 0 && pattern[q] != text[i]) {
			q = next[q-1];
		}

		if (pattern[q] == text[i]) {
			q ++;
		}

		if (q == m) {
			//printf("Pattern occurs with shift: %dn", (i-m+1));
			break;
		}
	}

	return i-q+1;
}

最后

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