R9-dp篇

class Solution {
    public int coinChange(int[] coins, int amount) {
        int n=coins.length;
        int [][] f=new int[n+1][amount+1];
        //除2防止下面+1溢出
        Arrays.fill(f[0],Integer.MAX_VALUE/2);
        f[0][0]=0;
        for (int i=0;i<n;i++){
            for (int c=0;c<=amount;c++){
                if(c<coins[i]) f[i+1][c]=f[i][c];
                else f[i+1][c]=Math.min(f[i][c],f[i+1][c-coins[i]]+1);
            }
        }
        int ret=f[n][amount];
        return ret<Integer.MAX_VALUE/2?ret:-1;
    }
}