Add step5

Author: colorbox

703/step5.cpp

@@ -0,0 +1,99 @@
+class KthLargest {
+public:
+  KthLargest(int k, vector<int>& nums) : capacity(k) {
+    for (int num: nums) {
+      if (preserved_nums.size() < capacity) {
+        push(num);
+        continue;
+      }
+      if (num < preserved_nums.front()) {
+        continue;
+      }
+      push(num);
+      if (preserved_nums.size() > capacity) {
+        pop();
+      }
+    }
+  }
+  
+  int add(int val) {
+    if (preserved_nums.empty()) {
+      preserved_nums.push_back(val);
+      return val;
+    }
+    if (preserved_nums.size() == capacity && preserved_nums.front() > val) {
+      return preserved_nums.front();
+    }
+    push(val);
+    if (preserved_nums.size() > capacity) {
+      pop();
+    }
+    return preserved_nums.front();
+  }
+private:
+  int capacity;
+  vector<int> preserved_nums;
+
+  int parent_index(int index) {
+    return (index - 1) / 2;
+  }
+
+  void sift_up_from_last() {
+    int index = preserved_nums.size() - 1;
+    while (index > 0) {
+      int parent_index_ = parent_index(index);
+      if (preserved_nums[index] >= preserved_nums[parent_index_]) {
+        break;
+      }
+      swap(preserved_nums[index], preserved_nums[parent_index_]);
+      index = parent_index_;
+    }
+  }
+
+  int left_child_index(int index) {
+    return index * 2 + 1;
+  }
+
+  int right_child_index(int index) {
+    return index * 2 + 2;
+  }
+
+  int min_child_index(int index) {
+    int left = left_child_index(index);
+    int right = right_child_index(index);
+    if (right >= preserved_nums.size()) {
+      return left;
+    }
+    if (preserved_nums[left] <= preserved_nums[right]) {
+      return left;
+    }
+    return right;
+  }
+
+  bool has_child(int index) {
+    return left_child_index(index) < preserved_nums.size();
+  }
+
+  void sift_down_from_root() {
+    int index = 0;
+    while (has_child(index)) {
+      int min_child_index_ = min_child_index(index);
+      if (preserved_nums[min_child_index_] >= preserved_nums[index]) {
+        break;
+      }
+      swap(preserved_nums[min_child_index_], preserved_nums[index]);
+      index = min_child_index_;
+    }
+  }
+
+  void push(int num) {
+    preserved_nums.push_back(num);
+    sift_up_from_last();
+  }
+
+  void pop() {
+    swap(preserved_nums.front(), preserved_nums.back());
+    preserved_nums.pop_back();
+    sift_down_from_root();
+  }
+};