diff --git a/src/problem/mod.rs b/src/problem/mod.rs
index cb4a126..d00e9a5 100644
--- a/src/problem/mod.rs
+++ b/src/problem/mod.rs
@@ -306,3 +306,5 @@ mod p3255_find_the_power_of_k_size_subarrays_ii;
 mod p3235_check_if_the_rectangle_corner_is_reachable;
 
 mod p3242_design_neighbor_sum_service;
+
+mod p540_single_element_in_a_sorted_array;
diff --git a/src/problem/p540_single_element_in_a_sorted_array.rs b/src/problem/p540_single_element_in_a_sorted_array.rs
new file mode 100644
index 0000000..b156d13
--- /dev/null
+++ b/src/problem/p540_single_element_in_a_sorted_array.rs
@@ -0,0 +1,43 @@
+/**
+ * [540] Single Element in a Sorted Array
+ */
+pub struct Solution {}
+
+// submission codes start here
+
+impl Solution {
+    pub fn single_non_duplicate(nums: Vec<i32>) -> i32 {
+        let n = nums.len();
+        let (mut left, mut right) = (0, n - 1);
+
+        while left < right {
+            let middle = (right - left) / 2 + left;
+            if nums[middle] == nums[middle ^ 1] {
+                left = middle + 1;
+            } else {
+                right = middle;
+            }
+        }
+
+        nums[left]
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_540() {
+        assert_eq!(
+            2,
+            Solution::single_non_duplicate(vec![1, 1, 2, 3, 3, 4, 4, 8, 8])
+        );
+        assert_eq!(
+            10,
+            Solution::single_non_duplicate(vec![3, 3, 7, 7, 10, 11, 11])
+        );
+    }
+}