[Leetcode] climbing stairs

You are climbing a stair case. It takesNSteps 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?

 

DP enlightened. After finishing this question, I finally got a rough idea of DP. I checked the table from the bottom up and it would be okay after the table is created. The complexity is O (n)

void iter(int acc, int n, vector<int> &table) {    if (acc < 0) return;    if (acc == n+1) return;    int a = acc-1 < 0? 0 : acc-1;    int b = acc-2 <0? 0 : acc-2;    table.push_back(table[a] + table[b]);    iter(acc+1, n, table);}int climbStairs(int n) {    vector<int> table;    table.push_back(0);    table.push_back(1);    table.push_back(2);    if (n < 3) return table[n];    iter(3, n,table);    return table[n];}

 

A pure recursive version is provided. Of course it is TLE's

int climbstairs_TLE(int n) {    if (n == 1) return 1;    if (n == 2) return 2;    return climbstairs_TLE(n-1) + climbstairs_TLE(n-2);}

Tle

 

[Leetcode] climbing stairs