代码随想录算法训练营20期|第四十五天|动态规划part07|● 70. 爬楼梯 （进阶）● 322. 零钱兑换 ● 279.完全平方数

•  70. 爬楼梯 （进阶）

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

•  322. 零钱兑换 

class Solution {
    public int coinChange(int[] coins, int amount) {
        int[] dp = new int[amount + 1];
        Arrays.fill(dp, amount + 1);
        dp[0] = 0;

        for (int coin : coins) {
            for (int j = coin; j <= amount; j++) {
                dp[j] = Math.min(dp[j], dp[j - coin] + 1);
            }
        }

        if (dp[amount] == amount + 1) {
            dp[amount] = -1;
        }
        return dp[amount];
    }
}

•  279.完全平方数 

class Solution {
    public int numSquares(int n) {
        int max = Integer.MAX_VALUE;
        int[] dp = new int[n + 1];
        for (int j = 0; j <= n; j++) {
            dp[j] = max;
        }
        dp[0] = 0;
        for (int j = 1; j <= n; j++) {
            for (int i = 1; i * i <= j; i++) {
                dp[j] = Math.min(dp[j], dp[j - i * i] + 1);
            }
        }
        return dp[n];
    }
}