322. Coin Change

322/step1.cpp

@@ -0,0 +1,29 @@
+/*
+
+Time Comprexity: O(n * m) (n: amount, m: coinsの長さ)
+Space Complexity: O(n)
+
+intでオーバーフローしてしまい、脊髄反射的にlongを使用したがDPの方向を変えればオーバーフローしなさそう
+*/
+class Solution {
+public:
+    int coinChange(vector<int>& coins, int amount) {
+        vector<long> coin_nums(amount + 1, numeric_limits<long>::max());
+        coin_nums[0] = 0;
+        for (long i = 0; i <= amount; ++i) {
+            if (coin_nums[i] == numeric_limits<long>::max()) {
+                continue;
+            }
+            for (const long coin : coins) {
+                if (i + coin > amount) {
+                    continue;
+                }
+                coin_nums[i + coin] = min(coin_nums[i] + 1, coin_nums[i + coin]);
+            }
+        }
+        if (coin_nums.back() == numeric_limits<long>::max()) {
+            return -1;
+        }
+        return coin_nums.back();
+    }
+};

322/step2.cpp

@@ -0,0 +1,27 @@
+/*
+DPの方向を変えてオーバーフローしないようにした。
+*/
+
+class Solution {
+public:
+    int coinChange(vector<int>& coins, int amount) {
+        vector<int> coin_nums(amount + 1, numeric_limits<int>::max());
+        coin_nums[0] = 0;
+        for (int to_coins = 1; to_coins <= amount; ++to_coins) {
+            for (const int coin : coins) {
+                int from_coins = to_coins - coin;
+                if (from_coins < 0) {
+                    continue;
+                }
+                if (coin_nums[from_coins] == numeric_limits<int>::max()) {
+                    continue;
+                }
+                coin_nums[to_coins] = min(coin_nums[from_coins] + 1, coin_nums[to_coins]);
+            }
+        }
+        if (coin_nums.back() == numeric_limits<int>::max()) {
+            return -1;
+        }
+        return coin_nums.back();
+    }
+};

322/step3.cpp

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+class Solution {
+public:
+    int coinChange(vector<int>& coins, int amount) {
+        vector<int> min_coins(amount + 1, numeric_limits<int>::max());
+        min_coins[0] = 0;
+        for (int to_price = 1; to_price <= amount; ++to_price) {
+            for (const int coin : coins) {
+                int from_price = to_price - coin;
+                if (from_price < 0) {
+                    continue;
+                }
+                if (min_coins[from_price] == numeric_limits<int>::max()) {
+                    continue;
+                }
+                min_coins[to_price] = min(min_coins[from_price] + 1, min_coins[to_price]);
+            }
+        }
+        if (min_coins.back() == numeric_limits<int>::max()) {
+            return -1;
+        }
+        return min_coins.back();
+    }
+};