0042 solved.

0042-Trapping-Rain-Water/cpp-0042/CMakeLists.txt

@@ -0,0 +1,7 @@
+cmake_minimum_required(VERSION 3.5)
+project(cpp_0042)
+
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
+
+set(SOURCE_FILES main5.cpp)
+add_executable(cpp_0042 ${SOURCE_FILES})

0042-Trapping-Rain-Water/cpp-0042/main.cpp

@@ -0,0 +1,50 @@
+/// Source : https://leetcode.com/problems/trapping-rain-water/description/
+/// Author : liuyubobobo
+/// Time   : 2018-09-16
+
+#include <iostream>
+#include <vector>
+
+using namespace std;
+
+
+/// Brute Force
+/// Time Complexity: O(n^2)
+/// Space Complexity: O(1)
+class Solution {
+public:
+    int trap(vector<int>& height) {
+
+        if(height.size() <= 2)
+            return 0;
+
+        int res = 0;
+        for(int i = 1; i < height.size() - 1; i ++) {
+            int lmax = height[i], rmax = height[i];
+            for (int l = i - 1; l >= 0; l --)
+                lmax = max(lmax, height[l]);
+            for(int r = i + 1; r < height.size(); r ++)
+                rmax = max(rmax, height[r]);
+            res += min(lmax, rmax) - height[i];
+        }
+        return res;
+    }
+};
+
+
+int main() {
+
+    vector<int> height1 = {0,1,0,2,1,0,1,3,2,1,2,1};
+    cout << Solution().trap(height1) << endl;
+    // 6
+
+    vector<int> height2 = {4,2,3};
+    cout << Solution().trap(height2) << endl;
+    // 1
+
+    vector<int> height3 = {4, 2, 0, 3, 2, 5};
+    cout << Solution().trap(height3) << endl;
+    // 9
+
+    return 0;
+}

0042-Trapping-Rain-Water/cpp-0042/main2.cpp

@@ -0,0 +1,68 @@
+/// Source : https://leetcode.com/problems/trapping-rain-water/description/
+/// Author : liuyubobobo
+/// Time   : 2018-09-16
+
+#include <iostream>
+#include <vector>
+
+using namespace std;
+
+
+/// Memory Search
+///
+/// Time Complexity: O(n)
+/// Space Complexity: O(n)
+class Solution {
+public:
+    int trap(vector<int>& height) {
+
+        if(height.size() <= 2)
+            return 0;
+
+        vector<int> rdp(height.size(), -1);
+        getR(0, height, rdp);
+
+        vector<int> ldp(height.size(), -1);
+        getL(height.size() - 1, height, ldp);
+
+        int res = 0;
+        for(int i = 0; i < height.size(); i ++)
+            res += min(ldp[i], rdp[i]) - height[i];
+        return res;
+    }
+
+private:
+    int getR(int index, const vector<int>& height, vector<int>& rdp){
+
+        if(index == height.size() - 1)
+            return rdp[index] = height[index];
+
+        return rdp[index] = max(height[index], getR(index + 1, height, rdp));
+    }
+
+    int getL(int index, const vector<int>& height, vector<int>& ldp){
+
+        if(index == 0)
+            return ldp[index] = height[index];
+
+        return ldp[index] = max(height[index], getL(index - 1, height, ldp));
+    }
+};
+
+
+int main() {
+
+    vector<int> height1 = {0,1,0,2,1,0,1,3,2,1,2,1};
+    cout << Solution().trap(height1) << endl;
+    // 6
+
+    vector<int> height2 = {4,2,3};
+    cout << Solution().trap(height2) << endl;
+    // 1
+
+    vector<int> height3 = {4, 2, 0, 3, 2, 5};
+    cout << Solution().trap(height3) << endl;
+    // 9
+
+    return 0;
+}

0042-Trapping-Rain-Water/cpp-0042/main3.cpp

@@ -0,0 +1,53 @@
+/// Source : https://leetcode.com/problems/trapping-rain-water/description/
+/// Author : liuyubobobo
+/// Time   : 2018-09-16
+
+#include <iostream>
+#include <vector>
+
+using namespace std;
+
+
+/// Dynamic Programming
+///
+/// Time Complexity: O(n)
+/// Space Complexity: O(n)
+class Solution {
+public:
+    int trap(vector<int>& height) {
+
+        if(height.size() <= 2)
+            return 0;
+
+        vector<int> rdp(height.size(), height.back());
+        for(int i = height.size() - 2; i >= 0; i --)
+            rdp[i] = max(height[i], rdp[i + 1]);
+
+        vector<int> ldp(height.size(), height[0]);
+        for(int i = 1; i < height.size(); i ++)
+            ldp[i] = max(height[i], ldp[i - 1]);
+
+        int res = 0;
+        for(int i = 0; i < height.size(); i ++)
+            res += min(ldp[i], rdp[i]) - height[i];
+        return res;
+    }
+};
+
+
+int main() {
+
+    vector<int> height1 = {0,1,0,2,1,0,1,3,2,1,2,1};
+    cout << Solution().trap(height1) << endl;
+    // 6
+
+    vector<int> height2 = {4,2,3};
+    cout << Solution().trap(height2) << endl;
+    // 1
+
+    vector<int> height3 = {4, 2, 0, 3, 2, 5};
+    cout << Solution().trap(height3) << endl;
+    // 9
+
+    return 0;
+}

0042-Trapping-Rain-Water/cpp-0042/main4.cpp

@@ -0,0 +1,57 @@
+/// Source : https://leetcode.com/problems/trapping-rain-water/description/
+/// Author : liuyubobobo
+/// Time   : 2018-09-16
+
+#include <iostream>
+#include <vector>
+
+using namespace std;
+
+
+/// Using Stack
+///
+/// Time Complexity: O(n)
+/// Space Complexity: O(n)
+class Solution {
+public:
+    int trap(vector<int>& height) {
+
+        if(height.size() <= 2)
+            return 0;
+
+        vector<int> stack;
+        int res = 0;
+        for(int i = 0; i < height.size(); i ++){
+            while(!stack.empty() && height[i] > height[stack.back()]){
+                int cur = stack.back();
+                stack.pop_back();
+                if(stack.empty())
+                    break;
+
+                int dis = i - stack.back() - 1;
+                int h = min(height[stack.back()], height[i]) - height[cur];
+                res += h * dis;
+            }
+            stack.push_back(i);
+        }
+        return res;
+    }
+};
+
+
+int main() {
+
+    vector<int> height1 = {0,1,0,2,1,0,1,3,2,1,2,1};
+    cout << Solution().trap(height1) << endl;
+    // 6
+
+    vector<int> height2 = {4,2,3};
+    cout << Solution().trap(height2) << endl;
+    // 1
+
+    vector<int> height3 = {4, 2, 0, 3, 2, 5};
+    cout << Solution().trap(height3) << endl;
+    // 9
+
+    return 0;
+}

0042-Trapping-Rain-Water/cpp-0042/main5.cpp

@@ -0,0 +1,60 @@
+/// Source : https://leetcode.com/problems/trapping-rain-water/description/
+/// Author : liuyubobobo
+/// Time   : 2018-09-16
+
+#include <iostream>
+#include <vector>
+
+using namespace std;
+
+
+/// Two Pointers
+///
+/// Time Complexity: O(n)
+/// Space Complexity: O(1)
+class Solution {
+public:
+    int trap(vector<int>& height) {
+
+        if(height.size() <= 2)
+            return 0;
+
+        int res = 0;
+        int l = 0, r = height.size() - 1, lmax_i = l, rmax_i = r;
+        while(l < r){
+            if(height[l] < height[r]){
+                l ++;
+                if(height[l] < height[lmax_i])
+                    res += min(height[lmax_i], height[rmax_i]) - height[l];
+                else
+                    lmax_i = l;
+            }
+            else{
+                r --;
+                if(height[r] < height[rmax_i])
+                    res += min(height[lmax_i], height[rmax_i]) - height[r];
+                else
+                    rmax_i = r;
+            }
+        }
+        return res;
+    }
+};
+
+
+int main() {
+
+    vector<int> height1 = {0,1,0,2,1,0,1,3,2,1,2,1};
+    cout << Solution().trap(height1) << endl;
+    // 6
+
+    vector<int> height2 = {4,2,3};
+    cout << Solution().trap(height2) << endl;
+    // 1
+
+    vector<int> height3 = {4, 2, 0, 3, 2, 5};
+    cout << Solution().trap(height3) << endl;
+    // 9
+
+    return 0;
+}

readme.md

@@ -80,6 +80,8 @@ email: [[email protected]](mailto:[email protected])
 | 039 | [Combination Sum](https://leetcode.com/problems/combination-sum/description/) | [无] | [C++](0039-Combination-Sum/cpp-0039/) | | |
 | 040 | [Combination Sum II](https://leetcode.com/problems/combination-sum-ii/description/) | [无] | [C++](0040-Combination-Sum-II/cpp-0040/) | | |
 | | | | | | |
+| 042 | [Trapping Rain Water](https://leetcode.com/problems/trapping-rain-water/description/) | [solution](https://leetcode.com/problems/trapping-rain-water/solution/) | [C++](0042-Trapping-Rain-Water/cpp-0042/) | | |
+| | | | | | |
 | 046 | [Permutations](https://leetcode.com/problems/permutations/description/) | [缺：排列算法整理] | [C++](0046-Permutations/cpp-0046/) | [Java](0046-Permutations/java-0046/src/) | |
 | 047 | [Permutations II](https://leetcode.com/problems/permutations-ii/description/) | [无] | [C++](0047-Permutations-II/cpp-0047/) | | |
 | 048 | [Rotate Image](https://leetcode.com/problems/rotate-image/description/) | [无] | [C++](0048-Rotate-Image/cpp-0048/) | | |