Merge pull request neetcode-gh#2762 from mdmzfzl/0239_Sliding_Window_Maximum

Added 0239-sliding-window-maximum.c

Author: mdmzfzl

c/0239-sliding-window-maximum.c

@@ -0,0 +1,84 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+typedef struct {
+    int value;
+    int index;
+} Pair;
+
+typedef struct {
+    Pair* data;
+    int front;
+    int rear;
+    int size;
+} Deque;
+
+// Create a new deque
+Deque* createDeque(int size) {
+    Deque* deque = (Deque*)malloc(sizeof(Deque));
+    deque->data = (Pair*)malloc(size * sizeof(Pair));
+    deque->front = 0;
+    deque->rear = -1;
+    deque->size = 0;
+    return deque;
+}
+
+// Push a new element to the back of the deque
+void pushBack(Deque* deque, int value, int index) {
+    while (deque->size > 0 && value >= deque->data[deque->rear].value) {
+        deque->rear--;
+        deque->size--;
+    }
+    deque->rear++;
+    deque->data[deque->rear].value = value;
+    deque->data[deque->rear].index = index;
+    deque->size++;
+}
+
+// Pop elements from the front of the deque
+void popFront(Deque* deque, int index) {
+    if (deque->size > 0 && deque->data[deque->front].index == index) {
+        deque->front++;
+        deque->size--;
+    }
+}
+
+// Calculate the maximum sliding window
+int* maxSlidingWindow(int* nums, int numsSize, int k, int* returnSize) {
+    // Check if the input array is empty
+    if (numsSize == 0) {
+        *returnSize = 0;
+        return NULL;
+    }
+
+    // Calculate the size of the result array
+    *returnSize = numsSize - k + 1;
+    
+    // Allocate memory for the result array
+    int* result = (int*)malloc((*returnSize) * sizeof(int));
+
+    // Create a deque (double-ended queue) to efficiently track maximum elements
+    Deque* deque = createDeque(numsSize);
+
+    // Iterate through the input array
+    for (int i = 0; i < numsSize; i++) {
+        // Push the current element to the deque, maintaining the maximum at the front
+        pushBack(deque, nums[i], i);
+
+        // Check if the window has reached the required size
+        if (i >= k - 1) {
+            // Store the maximum element in the result array
+            result[i - k + 1] = deque->data[deque->front].value;
+            
+            // Pop elements from the front of the deque that are outside the current window
+            popFront(deque, i - k + 1);
+        }
+    }
+
+    // Free memory allocated for the deque
+    free(deque->data);
+    free(deque);
+
+    // Return the result array containing maximum elements in each sliding window
+    return result;
+}