[leetcode]746. Min Cost Climbing Stairs
阿新 • • 發佈:2018-12-17
Solution 1:遞迴 tle
class Solution { public int minCostClimbingStairs(int[] cost) { int n=cost.length-1; int start=-1; return help(cost,start,n); } public int help(int[] cost,int i,int n){ if(i>n)return 0; if(i<0)return Math.min(help(cost,i+1,n),help(cost,i+2,n));; return cost[i]+Math.min(help(cost,i+1,n),help(cost,i+2,n)); } }
Solution 2: top down的dp
class Solution { public int minCostClimbingStairs(int[] cost) { int n=cost.length-1; int start=-1; int[] dp=new int[n+1]; Arrays.fill(dp,-1); return help(cost,start,n,dp); } public int help(int[] cost,int i,int n,int[] dp){ if(i>n)return 0; if(i<0)return Math.min(help(cost,i+1,n,dp),help(cost,i+2,n,dp));; if(dp[i]>0)return dp[i]; dp[i]=cost[i]+Math.min(help(cost,i+1,n,dp),help(cost,i+2,n,dp)); return dp[i]; } }
Solution 3: bottom up的dp
今天突然豁然開朗了top down和bottom up
top down就是最直接的遞迴,一層一層下去。
bottom up就是反著來
class Solution { public int minCostClimbingStairs(int[] cost) { int n=cost.length-1; int[] dp=new int[n+3]; dp[n+1]=0; dp[n+2]=0; for(int i=n;i>=0;i--){ dp[i]=cost[i]+Math.min(dp[i+1],dp[i+2]); } return Math.min(dp[0],dp[1]); } }