From 45219c11fbcdbaa4c70c8e7e9412556673b71442 Mon Sep 17 00:00:00 2001
From: Anmol Singh <anmolzaildar4@gmail.com>
Date: Thu, 16 Oct 2025 03:35:16 -0400
Subject: [PATCH] feat(sorts): add TournamentSort (winner-tree) [#6631]

---
 .../thealgorithms/sorts/TournamentSort.java   | 77 +++++++++++++++++++
 1 file changed, 77 insertions(+)
 create mode 100644 src/main/java/com/thealgorithms/sorts/TournamentSort.java

diff --git a/src/main/java/com/thealgorithms/sorts/TournamentSort.java b/src/main/java/com/thealgorithms/sorts/TournamentSort.java
new file mode 100644
index 000000000000..67b866bcd2a9
--- /dev/null
+++ b/src/main/java/com/thealgorithms/sorts/TournamentSort.java
@@ -0,0 +1,77 @@
+package com.thealgorithms.sorts;
+import java.util.Arrays;
+
+/**
+ * Tournament Sort (Winner Tree) – comparison-based sorting that repeatedly
+ * selects the minimum via a "winner tree" and removes it,
+ * updating winners along the path.
+ *
+ * Time: O(n log m) where m is next power-of-two ≥ n
+ */
+public final class TournamentSort {
+
+    private TournamentSort() {
+    }
+
+    public static <T extends Comparable<T>> void sort(T[] a) {
+        if (a == null || a.length < 2) return;
+
+        final int n = a.length;
+        int m = 1;
+        while (m < n) m <<= 1;
+
+        // Winner-tree nodes;
+        Node<T>[] tree = new Node[2 * m];
+
+        for (int i = 0; i < n; i++) {
+            int leafPos = m + i;
+            tree[leafPos] = new Node<>(a[i], leafPos);
+        }
+
+        for (int i = m - 1; i >= 1; i--) {
+            tree[i] = minNode(tree[2 * i], tree[2 * i + 1]);
+        }
+
+        T[] out = Arrays.copyOf(a, n);
+        for (int k = 0; k < n; k++) {
+            Node<T> winner = tree[1];
+            out[k] = winner.value;
+
+            // remove winner leaf by setting it to null (acts like +∞)
+            int pos = winner.leafPos;
+            tree[pos] = null;
+
+            // re-compute winners up the path
+            pos >>= 1;
+            while (pos >= 1) {
+                tree[pos] = minNode(tree[2 * pos], tree[2 * pos + 1]);
+                pos >>= 1;
+            }
+        }
+
+        System.arraycopy(out, 0, a, 0, n);
+    }
+    
+    public static void sort(int[] a) {
+        if (a == null || a.length < 2) return;
+        Integer[] boxed = new Integer[a.length];
+        for (int i = 0; i < a.length; i++) boxed[i] = a[i];
+        sort(boxed);
+        for (int i = 0; i < a.length; i++) a[i] = boxed[i];
+    }
+
+    private static <T extends Comparable<T>> Node<T> minNode(Node<T> left, Node<T> right) {
+        if (left == null) return right;
+        if (right == null) return left;
+        return (left.value.compareTo(right.value) <= 0) ? left : right;
+    }
+
+    private static final class Node<T extends Comparable<T>> {
+        final T value;
+        final int leafPos;
+        Node(T v, int p) {
+            this.value = v;
+            this.leafPos = p;
+        }
+    }
+}