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[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?

 

DP启蒙啊,做完这题终于对DP有个大概的认识了,自底向上检表,建完也就ok了,复杂度是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];}

 

另附纯递归版,当然是TLE的

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