Solved DP problems

coin-change-2.java

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+// Time Complexity :O(n^2)
+// Space Complexity : O(m*n)
+// Did this code successfully run on Leetcode : Yes
+// Three line explanation of solution in plain english
+
+// Your code here along with comments explaining your approach
+
+class Solution {
+    public int change(int amount, int[] coins) {
+        int m = coins.length;
+        int n = amount;
+
+        int[][] dp = new int[m + 1][n + 1];
+        dp[0][0] = 1;
+
+        for (int i = 1; i <= m; i++) {
+            for (int j = 0; j <= n; j++) {
+                if(j < coins[i-1]){
+                    dp[i][j] = dp[i-1][j];
+                } else{
+                    dp[i][j] = dp[i-1][j] + dp[i][j - coins[i-1]];
+                }
+            }
+        }
+        return dp[m][n];
+    }
+}

paint-house.java

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+public class PaintHouse {
+
+    public int minCost(int[][] costs) {
+        if (costs == null || costs.length == 0) {
+            return 0;
+        }
+
+        // Iterate bottom up from the second-to-last house to the first.
+        for (int i = costs.length - 2; i >= 0; i--) { 
+            // Min cost to paint house 'i' red is its original cost plus the
+            // min cost of painting house 'i+1' blue or green.
+            costs[i][0] += Math.min(costs[i + 1][1], costs[i + 1][2]);
+
+            // Min cost to paint house 'i' blue
+            costs[i][1] += Math.min(costs[i + 1][0], costs[i + 1][2]);
+
+            // Min cost to paint house 'i' green
+            costs[i][2] += Math.min(costs[i + 1][0], costs[i + 1][1]);
+        }
+        return Math.min(Math.min(costs[0][0], costs[0][1]), costs[0][2]);
+    }
+
+    public static void main(String[] args) {
+        PaintHouse solver = new PaintHouse();
+        int[][] costs = {{17, 2, 17}, {16, 16, 5}, {14, 3, 19}};
+
+        System.out.println("The minimum cost is: " + solver.minCost(costs)); // Expected output: 10
+    }
+}
+
+// Time Complexity : O(n)
+// Space Complexity : O(1)
+// Did this code successfully run on Leetcode : yes
+// Three line explanation of solution in plain english 
+// used the bottom up approach to calculate the minimum costs
+//stored the total cost in the row above
+//Chose the minimum from the first row
+
+// Your code here along with comments explaining your approach