1776

Author: mkmark

leetcode/1776/a.in

@@ -0,0 +1 @@
+[[1,2],[2,1],[4,3],[7,2]]

leetcode/1776/main.cpp

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+/*
+author: [email protected]
+*/
+
+#include <bits/stdc++.h>
+#include "../../lib/LeetCodeInput.hpp"
+#include "solution.cpp"
+using namespace std;
+
+int main()
+{
+    LeetCodeInput li("a.in");
+
+    vector<vector<int>> mat_1 = li.get_vvi(0);
+    // vector<int> arr_1 = li.get_vi(0);
+    // int num_1 = li.get_i(0);
+    // string s_1 = li.get_s(0);
+
+    chrono::steady_clock::time_point begin = chrono::steady_clock::now();
+    Solution solution;
+    auto output = solution.getCollisionTimes(mat_1);
+    chrono::steady_clock::time_point end = chrono::steady_clock::now();
+    cout << "Time difference = " << chrono::duration_cast<chrono::microseconds> (end - begin).count() << "µs" << endl;
+
+    // cout << output << endl;
+
+    for (int i: output){
+        cout << i << ' ';
+    }
+
+    // for (auto i: output){
+    //     for (int j: i){
+    //         cout << j << ' ';
+    //     }
+    //     cout << '\n';
+    // }
+
+    return 0;
+}

leetcode/1776/solution.cpp

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+/*
+author: [email protected]
+time: O(n2)
+space: O(n)
+
+Runtime: 488 ms, faster than 100.00% of C++ online submissions for Car Fleet II.
+Memory Usage: 129.9 MB, less than 25.36% of C++ online submissions for Car Fleet II.
+*/
+
+#include <bits/stdc++.h>
+
+using namespace std;
+
+#define all(x) begin(x), end(x)
+typedef vector<int> vi;
+typedef vector<vector<int>> vvi;
+
+class Solution {
+public:
+    vector<double> getCollisionTimes(vector<vector<int>>& cars) {
+        /// car = { b, k }
+        int n = size(cars);
+
+        vector<double> res(n);
+        /// envelop k and b
+        int k[100000];
+        double b[100000];
+        /// collision position of car ? and car i
+        double x[100000];
+
+        int env_size = 1;
+        res[n-1] = -1;
+        k[0] = cars[n-1][1];
+        b[0] = cars[n-1][0];
+
+        int j;
+        int k_i;
+        double b_i;
+        for (int i=n-2; i>-1; --i){
+            k_i = cars[i][1];
+            b_i = cars[i][0];
+            for (j = 0; j<env_size; ++j){
+                /// will never caught
+                if (k_i <= k[j]) break;
+                /// y = k1 x + b1
+                /// y = k2 x + b2
+                /// x = (b2 - b1)/(k1 - k2)
+                x[j] = (b[j] - b_i) / (k_i - k[j]);
+            }
+            if (j) {
+                /// use env_size to temp store the min element pos
+                env_size = min_element(x, x+j) - x;
+                res[i] = x[env_size];
+                /// the actual replacement happens after min element
+                ++env_size;
+            } else {
+                env_size = 0;
+                res[i] = -1;
+            }
+            k[env_size] = k_i;
+            b[env_size] = b_i;
+            /// the actual env_size
+            ++env_size;
+        }
+
+        return res;
+    }
+};
+
+const static auto initialize = [] {
+    std::ios::sync_with_stdio(false);
+    std::cin.tie(nullptr);
+    std::cout.tie(nullptr);
+    return nullptr;
+}();