代码随想录一刷day45

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前言

一、力扣70. 爬楼梯

class Solution {
    public int climbStairs(int n) {
        int[] dp = new int[n+1];
        int[] nums = new int[]{1, 2};
        dp[0] = 1;
        for(int i = 0 ; i <= n; i ++){
            for(int j = 0; j < 2; j ++){
                if(i >= nums[j]){
                    dp[i] += dp[i - nums[j]];
                }
            }
        }
        return dp[n];
    }
}

二、力扣322. 零钱兑换

class Solution {
    public int coinChange(int[] coins, int amount) {
        int max = Integer.MAX_VALUE;
        int[] dp = new int[amount + 1];
        for(int i = 0; i <= amount; i ++){
            dp[i] = max;
        }
        dp[0] = 0;
        for(int i = 0; i < coins.length; i ++){
            for(int j = coins[i]; j <= amount; j ++){
                if((dp[j - coins[i]]) != max){
                    dp[j] = Math.min(dp[j], dp[j - coins[i]] + 1);
                }
            }
        }
        return dp[amount] == max ? -1 : dp[amount];
    }
}

三、力扣279. 完全平方数

class Solution {
    public int numSquares(int n) {
        int[] nums = new int[(int)Math.sqrt(n) + 1];
        for(int i = 1; i < nums.length; i ++){
            nums[i] = i * i;
        }
        int max = Integer.MAX_VALUE;
        int[] dp = new int[n + 1];
        for(int i = 1; i <= n; i ++){
            dp[i] = max;
        }
        dp[1] = 1;
        for(int i = 1; i < nums.length; i ++){
            for(int j = nums[i]; j <= n; j ++){
                if(dp[j - nums[i]] != max){
                    dp[j] = Math.min(dp[j], dp[j - nums[i]] + 1);
                }
            }
        }
        return dp[n];
    }
}