minimum path falling sum DP

Author: unfixedbug

Dynamic Programming/minimumPathSumDP.java

@@ -0,0 +1,69 @@
+/*https://leetcode.com/problems/minimum-path-sum/
+ * dp easy, striver op
+ *
+ */
+
+private class Recursion {
+
+  public int minPathSum(int[][] grid) {
+    int n = grid.length;
+    int m = grid[0].length;
+    return recursion(n - 1, m - 1, grid);
+  }
+
+  private int recursion(int i, int j, int[][] grid) {
+    if (i == 0 && j == 0) return grid[0][0];
+    if (i < 0 || j < 0) return Integer.MAX_VALUE;
+    int up = recursion(i - 1, j, grid); // travelling from upside
+    int left = recursion(i, j - 1, grid); // travelling from righside
+    return grid[i][j] + Math.min(up, left);
+  }
+}
+
+private class memoization {
+  int dp[][];
+
+  public int minPathSum(int[][] grid) {
+    int n = grid.length;
+    int m = grid[0].length;
+    dp = new int[n][m];
+    for (int a[] : dp) {
+      Arrays.fill(a, -1);
+    }
+    return recursion(n - 1, m - 1, grid);
+  }
+
+  private int recursion(int i, int j, int[][] grid) {
+    if (i == 0 && j == 0) return grid[0][0];
+    if (i < 0 || j < 0) return Integer.MAX_VALUE;
+    if (dp[i][j] != -1) return dp[i][j];
+    int up = recursion(i - 1, j, grid); // travelling from upside
+    int left = recursion(i, j - 1, grid); // travelling from righside
+    return dp[i][j] = grid[i][j] + Math.min(up, left);
+  }
+}
+
+private class tabulation {
+  int dp[][];
+
+  public int minPathSum(int[][] grid) {
+    int n = grid.length;
+    int m = grid[0].length;
+    dp = new int[n][m];
+    for (int a[] : dp) {
+      Arrays.fill(a, -1);
+    }
+    for (int i = 0; i < n; i++) {
+      for (int j = 0; j < m; j++) {
+        if (i == 0 && j == 0) dp[i][j] = grid[i][j];
+        if (dp[i][j] != -1) continue; else if (i == 0 && j != 0) dp[i][j] =
+          grid[i][j] + dp[i][j - 1]; else if (i != 0 && j == 0) dp[i][j] =
+          grid[i][j] + dp[i - 1][j]; else {
+          dp[i][j] = grid[i][j] + Math.min(dp[i - 1][j], dp[i][j - 1]);
+        }
+      }
+    }
+
+    return dp[n - 1][m - 1];
+  }
+}