递归问题复习

目录

汉诺塔问题

求一组数中的第K大数

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汉诺塔问题

#include <stdio.h>
void Move(int n, char start, char goal,char temp) 
{
	if(n >= 1)
	{
		Move(n-1, start, temp, goal);
		printf("%c -> %c\n", start, goal);
		Move(n-1, temp, goal, start);
	}
}
int main()
{
	int n;
	scanf("%d", &n);
	char a = 'a' , b = 'b', c = 'c';
	Move(n, a, c, b);
	return 0;
}

求一组数中的第K大数

输入

9

6 5 9 8 2 1 7 3 4

5

 输出

5

输入

9

6 5 9 8 2 1 7 3 4

7 

输出

 3

#include <stdio.h>
#include <stdlib.h>
void swap(int *x, int *y);
int FindKthLargest(int s[], int K, int Left, int Right);
int main()
{
	int N;
	scanf("%d", &N);
	int *s;
	s = (int *)malloc(sizeof(int) * N);
	int i;
	for(i = 0; i < N; i++)
	{
		scanf("%d", &s[i]);
	}
	int K;
	scanf("%d", &K);
	printf("%d",FindKthLargest(s, K, 0, N-1));
	return 0;
 } 
void swap(int *x, int *y)
{
	int t;
	t = *x; *x = *y; *y = t;
}
int FindKthLargest(int s[], int K, int Left, int Right)
{
	int e = s[Left];
	int L = Left, R = Right;
    while(1)
	{
		while(s[Left] >= e) Left++;
		while(s[Right] < e) Right--;
		if(Left < Right) swap(&s[Left], &s[Right]);
		else break;
	}
	swap(&s[L], &s[Left-1]);
	if((Left-L) > K) 
	   return FindKthLargest(s, K, L, Left-2);
	else if((Left-L) < K)
	   return FindKthLargest(s, K-(Left-L), Left, R);
	else return e;
}