Triangle DP

Author: unfixedbug

Dynamic Programming/triangle.java

@@ -0,0 +1,43 @@
+/*https://leetcode.com/problems/triangle/
+ * triangle
+ * strivers dp series
+ */
+private class recursion {
+
+  public int minimumTotal(List<List<Integer>> tri) {
+    return recur(tri, 0, 0);
+  }
+
+  private static int recur(List<List<Integer>> tri, int i, int j) {
+    if (i == tri.size() - 1) {
+      return tri.get(i).get(j);
+    }
+    int ans = tri.get(i).get(j);
+    int down = recur(tri, i + 1, j); //tri.get(i+1).get(j);
+    int diagonal = recur(tri, i + 1, j + 1); //tri.get(i+1).get(j+1);
+    return ans + Math.min(down, diagonal);
+  }
+}
+
+private class memoization {
+  int dp[][];
+
+  public int minimumTotal(List<List<Integer>> tri) {
+    dp = new int[tri.size()][tri.size()];
+    for (int a[] : dp) {
+      Arrays.fill(a, -1);
+    }
+    return recur(tri, 0, 0);
+  }
+
+  private int recur(List<List<Integer>> tri, int i, int j) {
+    if (i == tri.size() - 1) {
+      return tri.get(i).get(j);
+    }
+    if (dp[i][j] != -1) return dp[i][j];
+    int ans = tri.get(i).get(j);
+    int down = recur(tri, i + 1, j); //tri.get(i+1).get(j);
+    int diagonal = recur(tri, i + 1, j + 1); //tri.get(i+1).get(j+1);
+    return dp[i][j] = ans + Math.min(down, diagonal);
+  }
+}