LeetCode 322 Coin Change (完全背包)

You are given coins of different denominations and a total amount of money
amount. Write a function to compute 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

.

Example 1:

coins =

[1, 2, 5]

, amount =

11

return

3

(11 = 5 + 5 + 1)

Example 2:

coins =

[2]

, amount =

3

return

-1

.

Note:

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

题目链接：https://leetcode.com/problems/coin-change/

题目分析：因为个数是无穷的，所以就是一个完全背包计数问题，dp[i]表示合到i所需要的最少个数，dp初始化为无穷大，dp[0] = 0

public class Solution {

public int coinChange(int[] coins, int amount) {
int[] dp = new int[amount + 1];
Arrays.fill(dp, Integer.MAX_VALUE);
dp[0] = 0;
for(int i = 0; i < coins.length; i ++) {
for(int j = 0; j <= amount; j ++) {
int pre = j - coins[i];
if(pre >= 0 && dp[pre] < Integer.MAX_VALUE) {
dp[j] = Math.min(dp[j], dp[pre] + 1);
}
}
}
if(dp[amount] == Integer.MAX_VALUE) {
return -1;
}
return dp[amount];
}
}