Solve #229

Author: aylei

src/lib.rs

@@ -196,3 +196,4 @@ mod n0225_implement_stack_using_queues;
 mod n0226_invert_binary_tree;
 mod n0227_basic_calculator_ii;
 mod n0228_summary_ranges;
+mod n0229_majority_element_ii;

src/n0229_majority_element_ii.rs

@@ -0,0 +1,76 @@
+/**
+ * [229] Majority Element II
+ *
+ * Given an integer array of size n, find all elements that appear more than ⌊ n/3 ⌋ times.
+ *
+ * Note: The algorithm should run in linear time and in O(1) space.
+ *
+ * Example 1:
+ *
+ *
+ * Input: [3,2,3]
+ * Output: [3]
+ *
+ * Example 2:
+ *
+ *
+ * Input: [1,1,1,3,3,2,2,2]
+ * Output: [1,2]
+ *
+ */
+pub struct Solution {}
+
+// submission codes start here
+
+impl Solution {
+    pub fn majority_element(nums: Vec<i32>) -> Vec<i32> {
+        if nums.is_empty() { return vec![] }
+        let (mut vote0, mut vote1, mut candidate0, mut candidate1) = (0, 0, -1, -2);
+        for &num in nums.iter() {
+            if num == candidate0 {
+                vote0 += 1;
+            } else if num == candidate1 {
+                vote1 += 1;
+            } else if vote0 == 0 {
+                candidate0 = num;
+                vote0 = 1;
+            } else if vote1 == 0 {
+                candidate1 = num;
+                vote1 = 1;
+            } else {
+                vote0 -= 1;
+                vote1 -= 1;
+            }
+        }
+        // the presents of majority element is not guaranteed, we have to do a double check
+        let mut res = Vec::new();
+        for &v in vec![candidate0, candidate1].iter() {
+            let mut count = 0;
+            for &num in nums.iter() {
+                if v == num {
+                    count += 1;
+                }
+            }
+            if count > (nums.len() / 3) as i32 {
+                res.push(v);
+            }
+        }
+        res
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_229() {
+        assert_eq!(Solution::majority_element(vec![1,1,1,2,2,2,3,3,3]), vec![]);
+        assert_eq!(Solution::majority_element(vec![1,1,1,2,2,3,3,3]), vec![1,3]);
+        assert_eq!(Solution::majority_element(vec![1]), vec![1]);
+        assert_eq!(Solution::majority_element(vec![5,6,6]), vec![6]);
+        assert_eq!(Solution::majority_element(vec![1,2,3,4]), vec![]);
+    }
+}