randomized-select

Author: gzc

C09-Medians-and-Order-Statistics/randomized-select.cpp

@@ -1,66 +1,47 @@
-/*************************************************************************
-	> File Name: randomized-select.cpp
-	> Author: Louis1992
-	> Mail: [email protected]
-	> Blog: http://gzc.github.io
-	> Created Time: Sun May 24 11:46:39 2015
- ************************************************************************/
 #include<iostream>
 #include<vector>
 using namespace std;
 
-class Solution {
-    
-    int kthSmallest(vector<int>& arr, int l, int r, int k)
-    {
-        
-        if (k > 0 && k <= r - l + 1)
-        {
-            int pos = randomPartition(arr, l, r);
-            
-            if (pos-l == k-1)
-            return arr[pos];
-            else if(pos-l > k-1)
-            return kthSmallest(arr, l, pos-1, k);
-            else
-            return kthSmallest(arr, pos+1, r, k-pos+l-1);
-        }
-        return INT_MAX;
-    }
-    
-    int partition(vector<int>& arr, int l, int r)
-    {
-        int x = arr[r], i = l;
-        for(int j = l; j <= r - 1; j++)
-        {
-            if (arr[j] <= x)
-            {
-                swap(arr[i], arr[j]);
-                i++;
-            }
+int partition(vector<int>& arr, int l, int r) {
+    int x = arr[r], i = l;
+    for (int j = l; j <= r - 1; j++) {
+        if (arr[j] <= x) {
+            swap(arr[i], arr[j]);
+            i++;
         }
-        swap(arr[i], arr[r]);
-        return i;
-    }
-    
-    int randomPartition(vector<int>& arr, int l, int r)
-    {
-        int n = r-l+1;
-        int pivot = rand() % n;
-        swap(arr[l + pivot], arr[r]);
-        return partition(arr, l, r);
     }
+    swap(arr[i], arr[r]);
+    return i;
+}
+
+int randomPartition(vector<int>& arr, int l, int r) {
+    int n = r - l + 1;
+    int pivot = rand() % n;
+    swap(arr[l + pivot], arr[r]);
+    return partition(arr, l, r);
+}
 
-public:
-    int findKthLargest(vector<int>& nums, int k) {
-        return kthSmallest(nums, 0, nums.size()-1, nums.size()-k+1);
+int kthSmallest(vector<int>& arr, int l, int r, int k) {
+    int pos = randomPartition(arr, l, r);
+    if (pos - l == k - 1) {
+        return arr[pos];
+    } else if (pos - l > k - 1) {
+        return kthSmallest(arr, l, pos - 1, k);
+    } else {
+        return kthSmallest(arr, pos+1, r, k-pos+l-1);
     }
-};
+}
+
+int kthSmallest(vector<int>& arr, int k) {
+    // TODO: Validate k is in valid range. 
+    return kthSmallest(arr, 0, arr.size() - 1, k);
+}
 
-int main()
-{
-    int arr[5] = {2,4,0,-2,8};
-    vector<int>v(arr, arr+5);
-    Solution s;
-    cout << s.findKthLargest(v, 2) << endl;
-}
+int main() {
+    vector<int>v{3,4,2,5,1};
+    cout << kthSmallest(v, 1) << endl;
+    cout << kthSmallest(v, 2) << endl;
+    cout << kthSmallest(v, 3) << endl;
+    cout << kthSmallest(v, 4) << endl;
+    cout << kthSmallest(v, 5) << endl;
+}