Fibonacci

just 复习些概念，写写点代码。。。

public static int f (int n) {
		
		if (n == 0) return 0;
		if (n == 1) return 1;
		
		return f(n - 1) + f(n - 2);
	}
	
	
	public static int f1 (int n) {
		if (n == 0) return 0;
		if (n == 1) return 1;
		
		int[] tempArr = new int[]{0,1};
		
		int temp = 0;
		
		for (int i = 2; i <= n; i ++) {
			temp = tempArr[0] + tempArr[1];
			
			tempArr[i % 2] = temp;
		}
		
		return temp;
		
	}
	
	public static int f2 (int n) {
		if (n == 0) return 0;
		if (n == 1) return 1;
		
		int[] arr = new int[n + 1];
		arr[0] = 0;
		arr[1] = 1;

		for (int i = 2; i <= n; i ++) {
			arr[i] = arr[i - 1] + arr[i - 2];
		}
		
		return arr[n - 1];
		
	}