Runtime: 0 ms, faster than 100.00% of C++ online submissions for Climbing Stairs.
Memory Usage: 8.9 MB, less than 5.88% of C++ online submissions for Climbing Stairs.
class Solution {
public:
std::unordered_map<int, long> storeage;
int climbStairs(int n) {
return help(n);
}
int help(int m){
if(m == 0 || m ==1)
return 1;
else{
if(storeage.find(m) != storeage.end()){
return storeage[m];
}else{
storeage.insert(std::pair<int, long>(m, help(m-1)+help(m-2)));
return storeage[m];
}
}
}
};
动态规划的思想很好想,但是用递归的方法不停调用函数,不停进栈,内存占用多时间长,一个方法就是为了避免重复计算,用hash表保存下来曾经计算过的数值大大减小了计算量,时间加快,但是内存挺大的,还有其他的方法。