- 有數量不限的硬幣,幣值爲25分、10分、5分和1分,請編寫代碼計算n分有幾種表示法。給定一個int n,請返回n分有幾種表示法。保證n小於等於100000,爲了防止溢出,請將答案Mod 1000000007。
- 測試樣例: 6 返回:2
class Coins {
public:
int countWays(int n) {
// write code here
int coins[4]={1,5,10,25};
int dp[100001] = {0};
dp[0] = 1;
for(int i = 0;i < 4;++i){
for(int j = coins[i];j <= n;++j){
dp[j] =(dp[j]+dp[j-coins[i]])%1000000007;
}
}
return dp[n];
}
};
- 更好理解的代碼是下面這樣的,可是時間複雜度比較高:
public class Coins {
//硬幣的面值爲: 25,10,5,1
public int countWays(int n) {
return totalWays(n, 25);
}
public int totalWays(int remain, int curr){
int next = 0;
int ways = 0;
switch (curr){
case 25:
next = 10;
break;
case 10:
next = 5;
break;
case 5:
next = 1;
break;
case 1:
return 1; //注意若是next是1的話,那麼也就只有一種方法了
}
for(int i = 0; curr * i <= remain; i++){
ways += totalWays(remain - curr * i, next);
}
return ways%1000000007;
}
}