代码随想录二刷day45

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前言

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一、力扣70. 爬楼梯

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

二、力扣322. 零钱兑换

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

三、力扣279. 完全平方数

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