To add Suffix array algorithm implementation (#6530)

* adding Suffix Array Implementation

* adding test for Suffix Array

* patch: lint fix in SuffixArray.java

* patch: lint fix in SuffixArrayTest.java

* fix: private constructor update

* patch: lint fix in suffix array impl

* fix: lint issue line blankspace removal

* fix: checkstype issue

* fix: lint format issue

* Update DIRECTORY.md

src/main/java/com/thealgorithms/strings/SuffixArray.java

@@ -0,0 +1,60 @@
+package com.thealgorithms.strings;
+
+import java.util.Arrays;
+
+/**
+ * Suffix Array implementation in Java.
+ * Builds an array of indices that represent all suffixes of a string in sorted order.
+ * Wikipedia Reference: https://en.wikipedia.org/wiki/Suffix_array
+ * Author: Nithin U.
+ * Github: https://github.com/NithinU2802
+ */
+
+public final class SuffixArray {
+
+    private SuffixArray() {
+    }
+
+    public static int[] buildSuffixArray(String text) {
+        int n = text.length();
+        Integer[] suffixArray = new Integer[n];
+        int[] rank = new int[n];
+        int[] tempRank = new int[n];
+
+        // Initial ranking based on characters
+        for (int i = 0; i < n; i++) {
+            suffixArray[i] = i;
+            rank[i] = text.charAt(i);
+        }
+
+        for (int k = 1; k < n; k *= 2) {
+            final int step = k;
+
+            // Comparator: first by rank, then by rank + step
+            Arrays.sort(suffixArray, (a, b) -> {
+                if (rank[a] != rank[b]) {
+                    return Integer.compare(rank[a], rank[b]);
+                }
+                int ra = (a + step < n) ? rank[a + step] : -1;
+                int rb = (b + step < n) ? rank[b + step] : -1;
+                return Integer.compare(ra, rb);
+            });
+
+            // Re-rank
+            tempRank[suffixArray[0]] = 0;
+            for (int i = 1; i < n; i++) {
+                int prev = suffixArray[i - 1];
+                int curr = suffixArray[i];
+                boolean sameRank = rank[prev] == rank[curr] && ((prev + step < n ? rank[prev + step] : -1) == (curr + step < n ? rank[curr + step] : -1));
+                tempRank[curr] = sameRank ? tempRank[prev] : tempRank[prev] + 1;
+            }
+
+            System.arraycopy(tempRank, 0, rank, 0, n);
+
+            if (rank[suffixArray[n - 1]] == n - 1) {
+                break;
+            }
+        }
+        return Arrays.stream(suffixArray).mapToInt(Integer::intValue).toArray();
+    }
+}