算法：找零钱322. Coin Change

Posted 2021-09-23 架构师易筋

# 322. Coin Change
You are given an integer array coins representing coins of different denominations and an integer amount representing a total amount of money.

Return the fewest number of coins that you need to make up that amount. If that amount of money cannot be made up by any combination of the coins, return -1.

You may assume that you have an infinite number of each kind of coin.

Example 1:

Input: coins = [1,2,5], amount = 11
Output: 3
Explanation: 11 = 5 + 5 + 1

Example 2:

Input: coins = [2], amount = 3
Output: -1

Example 3:

Input: coins = [1], amount = 0
Output: 0

Example 4:

Input: coins = [1], amount = 1
Output: 1

Example 5:

Input: coins = [1], amount = 2
Output: 2

Constraints:

1 <= coins.length <= 12
1 <= coins[i] <= 231 - 1
0 <= amount <= 104

动态规划解法

动态规划转换公式dp[i] = Math.min(dp[i], dp[i - coin] + 1);。
这里的要点是，如果有值，那么一定要比默认值小。并且要遍历完所有的值。

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 i = 1; i <= amount; i++) {
            for (int coin: coins) {
                if (i - coin >= 0) {
                    dp[i] = Math.min(dp[i], dp[i - coin] + 1);
                }
            }
        }
        
        return dp[amount] != amount + 1 ? dp[amount] : -1;
    }
}