746. Min Cost Climbing Stairs

Problem Statement

You are given an integer array cost where cost[i] is the cost of ith step on a staircase. Once you pay the cost, you can either climb one or two steps.

You can either start from the step with index 0, or the step with index 1.

Return the minimum cost to reach the top of the floor.

Example 1:

Input: cost = [10,15,20]
Output: 15
Explanation: You will start at index 1.
- Pay 15 and climb two steps to reach the top.
The total cost is 15.

Example 2:

Input: cost = [1,100,1,1,1,100,1,1,100,1]
Output: 6
Explanation: You will start at index 0.
- Pay 1 and climb two steps to reach index 2.
- Pay 1 and climb two steps to reach index 4.
- Pay 1 and climb two steps to reach index 6.
- Pay 1 and climb one step to reach index 7.
- Pay 1 and climb two steps to reach index 9.
- Pay 1 and climb one step to reach the top.
The total cost is 6.

Constraints:

2 <= cost.length <= 1000
0 <= cost[i] <= 999

Intuition

Approach:

Recursively travel and find out the answer

Links

https://leetcode.com/problems/min-cost-climbing-stairs/description/?envType=daily-question&envId=2023-10-13

Video Links

Approach 1:

C++

class Solution {
public:
    vector<int> dp;
    int find_ans(vector<int> &cost, int index){
        if(index <= 1)
            return 0;

        if(dp[index] != -1)
            return dp[index];

        int one_step = cost[index-1] + find_ans(cost, index-1);
        int two_step = cost[index-2] + find_ans(cost, index-2);

        return dp[index] = min(one_step, two_step);
    }

    int minCostClimbingStairs(vector<int>& cost) {
        int n = cost.size();
        dp = vector<int> (n+1,-1);

        return find_ans(cost, n);
    }
};

Approach 2:

C++

class Solution {
public:
    vector<int> dp;
    int minCostClimbingStairs(vector<int>& cost) {
        int n = cost.size();
        dp = vector<int> (n+1,0);

        for(int i=2; i<=n; i++){
            int one_step = cost[i-1] + dp[i-1];
            int two_step = cost[i-2] + dp[i-2];

            dp[i] = min(one_step, two_step);
        }

        return dp[n];
    }
};

Approach 3:

C++

Approach 4:

C++