【题解】【DP】【Leetcode】Climbing Stairs

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?

思路：

最简单的DP问题：递归+查表

代码:

int climbStairs(int n) {
    vector<int> memo(n+1, -1);//忘了在memo[0]没有意义的时候，数组初始大小加一。。。
    return climb(n, memo);
}

int climb(int n, vector<int>& memo){//忘了加&，就会Time Limit Exceeded
    if(n < 0){
        return -1;
    }
    else if(n <= 2){
        memo[n] = n;
        return n;
    }
    
    if (memo[n-1] == -1)
        memo[n-1] = climb(n-1, memo);//修改了递归函数名之后没有更改其他函数体中的引用
    if(memo[n-2] == -1)
        memo[n-2] = climb(n-2, memo);
    //return memo[n-1] + 2*memo[n-2];//等等，子问题中好像有重叠
    return memo[n-1] + memo[n-2];
}