June9,10,11: daily challenge [M]

daily/June10.cpp

@@ -0,0 +1,27 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+class Solution {
+ public:
+ /**
+  * @brief LC: 881: Boats to save people
+  * GREEDY: Time: O(nlogn), Space: O(logn)
+  * 
+  * @param people 
+  * @param limit 
+  * @return int 
+  */
+  int numRescueBoats(vector<int>& people, int limit) {
+    int len = people.size();
+    int le = 0, ri = len - 1;
+    int ans = 0;
+    while (le <= ri) {
+      if (people[le] + people[ri] <= limit) {
+        le++;
+      }
+      ri--;
+      ans++;
+    }
+    return ans;
+  }
+};

daily/June11.cpp

@@ -0,0 +1,25 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+class Solution {
+ public:
+  /**
+   * @brief LC: 419: Battleships in board
+   * Time: O(mn), Space: O(1)
+   *
+   * @param board
+   * @return int
+   */
+  int countBattleships(vector<vector<int>>& board) {
+    int ans = 0;
+    for (int i = 0; i < board.size(); i++) {
+      for (int j = 0; j < board[0].size(); j++) {
+        if (board[i][j] == 'X' && (j == 0 || board[i][j - 1] != 'X') &&
+            (i == 0 || board[i - 1][j] != 'X')) {
+          ans++;
+        }
+      }
+    }
+    return ans;
+  }
+};

daily/June9.cpp

@@ -0,0 +1,33 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+class Solution {
+ public:
+  /**
+   * @brief LC: 312: Burst Ballons [H][M]
+   * Time: O(N^3), Space: O(N^2)
+   *
+   * @param nums
+   * @return int
+   */
+  int maxCoins(vector<int>& nums) {
+    int n = nums.size();
+    vector<vector<int>> rec(n + 2, vector<int>(n + 2));
+    vector<int> val(n + 2);
+    val[0] = val[n + 1] = 1;
+
+    for (int i = 1; i <= n; i++) {
+      val[i] = nums[i - 1];
+    }
+    for (int i = n - 1; i >= 0; i--) {
+      for (int j = i + 2; j <= n + 1; j++) {
+        for (int k = i + 1; k < j; k++) {
+          int sum = val[i] * val[k] * val[j];
+          sum += rec[i][k] + rec[k][j];
+          rec[i][j] = max(rec[i][j], sum);
+        }
+      }
+    }
+    return rec[0][n + 1];
+  }
+};