Main322.java

package HOT100;

import java.util.Arrays;

public class Main322 {
    public int coinChange(int[] coins, int amount) {
        if(amount < 1) {
            return 0;
        }
        return coinChange(coins, amount, new int[amount]);
    }

    private int coinChange(int[] coins, int amount, int[] count) {
        if(amount < 0) {
            return -1;
        }
        if(amount == 0) {
            return 0;
        }
        if(count[amount - 1] != 0) { // 剪枝
            return count[amount - 1];
        }
        int min = Integer.MAX_VALUE;
        for (int coin : coins) {
            int res = coinChange(coins, amount - coin, count);
            if(res >= 0 && res < min) {
                min = 1 + res;
            }
        }
        count[amount - 1] = (min == Integer.MAX_VALUE) ? -1 : min;
        return count[amount - 1];
    }
}


/**
 * 动态规划
 */
class Main322_1 {
    public int coinChange(int[] coins, int amount) {
        int max = amount + 1;
        int[] dp = new int[amount + 1];
        Arrays.fill(dp, max);
        dp[0] = 0;
        for (int i = 1; i <= amount; i++) {
            for (int j = 0; j < coins.length; j++) {
                if(coins[j] <= i) {
                    dp[i] = Math.min(dp[i], dp[i - coins[j]] + 1);
                }
            }
        }
        return dp[amount] > amount ? -1 : dp[amount];
    }
}