DP:给定硬币面值，以及总价钱，求利用最少硬币数保证达到总价钱，

public static int coinChange(int[] coins, int amount) {
        if (coins==null||coins.length==0||amount<0) {
            return -1;
        }
        int[][] dp = new int[coins.length][amount+1];
        int max = Integer.MAX_VALUE;
        for (int i = 1; i < dp[0].length; i++) {
            dp[0][i] = max;
            if ((i-coins[0])>=0&&(dp[0][i-coins[0]]!=max)) {
                dp[0][i] = dp[0][i-coins[0]]+1;
            }
        }
        for (int i = 1; i < dp.length; i++) {
            for (int j = 1; j <dp[0].length; j++) {
                int temp = max;
                if ((j-coins[i])>=0&&(dp[i][j-coins[i]]!=max)) {

                    temp = dp[i][j-coins[i]]+1;
                }
                dp[i][j] = Math.min(temp, dp[i-1][j]);
            }
        }
        return dp[coins.length-1][amount]!=max?dp[coins.length-1][amount]:-1;
    }