动态规划

You are climbing a stair case. It takes n steps to reach to the top.

Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?

上楼梯、斐波那契数列、泰波那契序列问题。

常规解法

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function f (n) {if (n<=2) {return n;} return f(n-1)+f(n-2);}

闭包，memory cache

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var gen = () => {
	let memory = [];
	return function fib(n) {
		if (n <= 1) {
			return 1;	
		}
		if (memory[n] > 0) {
			return memory[n];
		}
		let num = fib(n-1) + fib(n-2);
		memory[n] = num;
		return num;
	}
}

深度优先搜索

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var fff = (n) => {
	let memory = [0];
	for(let i = 1; i <= n; i++) {
		if (i <= 2) {
			memory[i] = i;
		} else {
			memory[i] = memory[i-1] + memory[i-2];
		}
	}
	return memory[n];
}