DP-2 complete

CoinChange2.java

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+// https://leetcode.com/problems/coin-change-ii/
+// Approach: Similar to Coin Change I
+// Optimize space using 1D array
+// Time: O(coins.length * amount)
+// Space: O(amount)
+class Solution {
+    public int change(int amount, int[] coins) {
+        int[] dp = new int[amount + 1];
+        dp[0] = 1; // one way to make the amount = 0 with zero coins (not choose)
+        for (int column = 1; column <= amount; column ++) {
+            // There are zero ways to make the amount > 0 with zero coins.
+            dp[column] = 0;
+        }
+        for (int row = 1; row <= coins.length; row ++) {
+            for (int column = 0; column <= amount; column ++) {
+                if (coins[row - 1] <= column) { // Denomation should be greater than or equal to amount
+                    dp[column] = dp[column] + dp[column - coins[row - 1]]; // Total number of ways
+                }
+            }
+        }
+        return dp[amount];
+    }
+}

PaintHouse.java

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+// Approach: Initialze costs of each color to paint the first house.
+// Iterate through the next rows/houses and consider each color + min(previous house colors)
+// Time complexity: O(N); N = costs.length
+// Space complexity: O(1)
+public class PaintHouse {
+    public int minCost(int[][] costs) {
+        int costRed = costs[0][0]; // 17 // 18 // 21
+        int costBlue = costs[0][1]; // 2 // 33 // 10
+        int costGreen = costs[0][2]; // 17 // 7 // 37
+        for (int i = 1; i < costs.length; i ++) {
+            int prevCostRed = costRed;
+            int prevCostBlue = costBlue;
+            int prevCostGreen = costGreen;
+            costRed = costs[i][0] + Math.min(prevCostBlue, prevCostGreen); // 16 + 2 // 14 + 7
+            costBlue = costs[i][1] + Math.min(prevCostRed, prevCostGreen); // 16 + 17 // 3 + 7
+            costGreen = costs[i][2] + Math.min(prevCostRed, prevCostBlue); // 5 + 2 // 19 + 18
+        }
+        return Math.min(costRed, Math.min(costBlue, costGreen)); // min of 21, 10, 7 = 7
+    }
+
+    public static void main(String[] args) {
+        PaintHouse paintHouse = new PaintHouse();
+        int[][] costs1 = new int[][] {{17, 2, 17}, {16, 16, 5}, {14, 3, 19}};
+        System.out.println(paintHouse.minCost(costs1));
+        int[][] costs2 = new int[][] {{7,6,2}};
+        System.out.println(paintHouse.minCost(costs2));
+        int[][] costs3 = new int[][] {{17, 10, 18}, {16, 14, 15}, {11, 10, 19}, {20, 5, 7}};
+        System.out.println(paintHouse.minCost(costs3));
+    }
+}