Merge pull request #5 from Subham1999/back_tracking

Back tracking

Author: Subham1999

.idea/workspace.xml

@@ -27,6 +27,12 @@
             <artifactId>rxjava</artifactId>
             <version>3.1.8</version>
         </dependency>
+        <!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-api -->
+        <dependency>
+            <groupId>org.slf4j</groupId>
+            <artifactId>slf4j-api</artifactId>
+            <version>2.0.16</version>
+        </dependency>
     </dependencies>
     <build>
         <plugins>

pom.xml

@@ -0,0 +1,61 @@
+package com.thealgorithm.backtracking;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+/**
+ * @author: Subham Santra
+ */
+public class CombinationSumII {
+  static class Solution {
+    public List<List<Integer>> combinationSum2(int[] candidates, int target) {
+      List<List<Integer>> result = new ArrayList<>();
+
+      Arrays.sort(candidates);
+      helper(candidates, 0, 0, target, result, new ArrayList<>());
+
+      return result;
+    }
+
+    void helper(
+        final int[] arr,
+        final int i,
+        final int sum,
+        final int target,
+        final List<List<Integer>> result,
+        final List<Integer> currentSet) {
+
+      if (sum > target) {
+        return;
+      }
+
+      if (sum == target) {
+        result.add(new ArrayList<>(currentSet));
+        return;
+      }
+
+      if (i == arr.length) {
+        return;
+      }
+
+      // include
+      currentSet.addLast(arr[i]);
+      helper(arr, i + 1, sum + arr[i], target, result, currentSet);
+      currentSet.removeLast();
+
+      // exclude : not only the current index also all the indexes having same value
+      // This is required because we want to remove the duplicate set
+      // 1 2 2 2 2 2 5
+      // When we have found {1, 2[1], 2[2]} we shall not add {1, 2[1], 2[3]} ... etc.
+      int j = i;
+      while (j < arr.length && arr[j] == arr[i]) ++j;
+      helper(arr, j, sum, target, result, currentSet);
+    }
+  }
+
+  public static void main(String[] args) {
+    System.out.println(new Solution().combinationSum2(new int[] {2, 5, 2, 1, 2}, 5));
+    System.out.println(new Solution().combinationSum2(new int[] {2, 2, 2, 2, 2, 2, 4, 4, 4, 4, 8, 7, 1, 1}, 8));
+  }
+}

src/main/java/com/thealgorithm/backtracking/CombinationSumII.java

@@ -0,0 +1,66 @@
+package com.thealgorithm.backtracking;
+
+/**
+ * @author: Subham Santra
+ */
+public class WordSearch {
+  public boolean exist(char[][] board, String word) {
+    final int m = board.length;
+    final int n = board[0].length;
+    final boolean[][] taken = new boolean[m][n];
+
+    for (int i = 0; i < m; ++i) {
+      for (int j = 0; j < n; ++j) {
+        if (board[i][j] == word.charAt(0)) {
+          if (EXPLORE(board, i, j, m, n, 0, word, taken)) {
+            return true;
+          }
+        }
+      }
+    }
+
+    return false;
+  }
+
+  boolean EXPLORE(
+      char[][] board,
+      int i,
+      int j,
+      int m,
+      int n,
+      int wordCharIndex,
+      String word,
+      boolean[][] taken) {
+    if (wordCharIndex == word.length()) {
+      return true;
+    }
+
+    if (!((0 <= i && i < m) && (0 <= j && j < n))) {
+      return false;
+    }
+
+    if (taken[i][j]) {
+      return false;
+    }
+
+    boolean ans = false;
+
+    taken[i][j] = true;
+    if (board[i][j] == word.charAt(wordCharIndex)) {
+      // We will explore further
+      ans |= EXPLORE(board, i, j + 1, m, n, wordCharIndex + 1, word, taken);
+      ans |= EXPLORE(board, i, j - 1, m, n, wordCharIndex + 1, word, taken);
+      ans |= EXPLORE(board, i + 1, j, m, n, wordCharIndex + 1, word, taken);
+      ans |= EXPLORE(board, i - 1, j, m, n, wordCharIndex + 1, word, taken);
+    }
+    taken[i][j] = false;
+    return ans;
+  }
+
+  public static void main(String[] args) {
+    char[][] board = {{'A', 'B', 'C', 'E'}, {'S', 'F', 'C', 'S'}, {'A', 'D', 'E', 'E'}};
+    System.out.println(new WordSearch().exist(board, "ABCCED"));
+    System.out.println(new WordSearch().exist(board, "ABCF"));
+    System.out.println(new WordSearch().exist(board, "SEE"));
+  }
+}