Day32 动态规划1 | LeetCode 509. 斐波那契数, 70. 爬楼梯, 746. 使用最小花费爬楼梯

LeetCode 509. 斐波那契数

class Solution {
public:
int dp[31];
    int fib(int n) {
        dp[1] = 1;
        for (int i = 2; i <= n;i++){
            dp[i] = dp[i - 1] + dp[i - 2];
        }
        return dp[n];

    }
};

LeetCode 70. 爬楼梯

class Solution {
public:
int dp[46];
    int climbStairs(int n) {
        dp[1] = 1;
        dp[2] = 2;
        for (int i = 3; i <= n; i++){
            dp[i] = dp[i - 1] + dp[i - 2];
        }
        return dp[n];
    }
};

LeetCode 746. 使用最小花费爬楼梯

class Solution {
public:

    int minCostClimbingStairs(vector<int>& cost) {
        int length = cost.size();
        int* dp = new int[length + 1];
        dp[0] = 0;
        dp[1] = 0;
        for (int i = 2; i < length + 1; i++){
            dp[i] = min(dp[i - 1] + cost[i - 1], dp[i - 2] + cost[i - 2]);
        }
        return dp[length];
    }
};

version 2（不用申请额外空间）

class Solution {
public:

    int minCostClimbingStairs(vector<int>& cost) {
        int length = cost.size();
        int dp0 = 0;
        int dp1 = 0;
        int dp = 0;
        for (int i = 2; i < length + 1; i++){
            dp = min(dp0 + cost[i - 2], dp1 + cost[i - 1]);
            dp0 = dp1;
            dp1 = dp;
        }
        return dp;
    }
};