322. Coin Change (DP)

 1 //70%
 2 class Solution {
 3     public int coinChange(int[] coins, int amount) {
 4         if(amount == 0) return 0;
 5         int[]res = new int[amount + 1];
 6         for(int i = 0; i <= amount; i++) {
 7             res[i] = Integer.MAX_VALUE;
 8         }
 9         /**
10          * 下面不用也可以
11          */
12         for(int i = 0; i < coins.length; i++) {
13             if(coins[i] <= amount) {   //coin超过amount没有用，也会超过res的bound 所以不用赋值
14                 res[coins[i]] = 1;
15             }    
16         }
17         for(int j = 1; j <= amount; j++) {
18             if(res[j] == 1) continue;
19             for(int i = 0; i < coins.length; i++) {
20                 if(coins[i] < j && res[j - coins[i]] != -1) {
21                     res[j] = Math.min(res[j], res[j - coins[i]] + 1);
22                 }
23             }
24             if(res[j] == Integer.MAX_VALUE) res[j] = -1;
25         }
26         
27         return res[amount];
28     }
29 }
30 
31 
32 //30%
33 
34 class Solution {
35     public int coinChange(int[] coins, int amount) {
36         if(amount == 0) return 0;
37         int[]res = new int[amount + 1];
38         for(int i = 0; i <= amount; i++) {
39             res[i] = Integer.MAX_VALUE;
40         }
41         res[0] = 0;
42         for(int j = 1; j <= amount; j++) {
43             for(int coin : coins) {
44                 if(coin <= j && res[j - coin] != -1) {
45                     res[j] = Math.min(res[j], res[j - coin] + 1);
46                 }
47             }
48             if(res[j] == Integer.MAX_VALUE) res[j] = -1;
49         }
50         
51         return res[amount];
52     }
53 }