741

leetcode/hard/741.cc

@@ -0,0 +1,60 @@
+#include <iostream>
+#include <vector>
+
+using std::vector;
+
+using std::cout; using std::endl;
+
+class Solution {
+public:
+    int cherryPickup(vector<vector<int>>& grid) {
+        int n = grid.size();
+        int dp[2 * n - 1][n][n];
+        memset(dp, 0xFF, sizeof(dp));
+        dp[2 * n - 2][n - 1][n - 1] = 0;
+        dp[0][0][0] = grid[0][0];
+        for (int k = 1; k < 2 * n - 1; k++) {
+            for (int x1 = 0; x1 <= k && x1 < n; x1++) {
+                for (int x2 = 0; x2 <= k && x2 < n; x2++) {
+                    int y1 = k - x1, y2 = k - x2;
+                    // current coordinate is rock
+                    if (grid[x1][y1] == -1 || grid[x2][y2] == -1) continue;
+                    for (int i = 0; i < 4; i++) {
+                        int x1_ = x1 + dx1[i], x2_ = x2 + dx2[i];
+                        int y1_ = k - 1 - x1_, y2_ = k - 1 - x2_;
+                        // previous coordinate is not valid
+                        if (x1_ < 0 || x2_ < 0 || y1_ < 0 || y2_ < 0) continue;
+                        // previous coordinate is rock
+                        if (grid[x1_][y1_] == -1 || grid[x2_][y2_] == -1) continue;
+                        // previous state is not reachable
+                        if (dp[k - 1][x1_][x2_] == -1) continue;
+                        int delta = x1 == x2 ? grid[x1][y1] : grid[x1][y1] + grid[x2][y2];
+                        dp[k][x1][x2] = std::max(dp[k][x1][x2], dp[k - 1][x1_][x2_] + delta);
+                    }
+                }
+            }
+        }
+        return dp[2 * n - 2][n - 1][n - 1];
+    }
+
+private:
+    int dx1[4] = {0, -1, 0, -1};
+    int dx2[4] = {0, 0, -1, -1};
+};
+
+// (0, 0) -> (n - 1, n - 1) -> (0, 0) == (0, 0) -> (n - 1, n - 1) 2 times == 2 people start at (0, 0) at the same time
+// dp[k][x1][x2] means max cherries from (0, 0) to (x1, y1) and (x2, y2) at k steps
+// dp[0][0][0] = grid[0][0]
+// dp[k][x1][x2] = max(dp[k - 1][x1][x2] + delta, dp[k - 1][x1 - 1][x2] + delta, dp[k - 1][x1][x2 - 1] + delta, dp[k - 1][x1 - 1][x2 - 1] + delta)
+
+int main() {
+    Solution* sol = new Solution();
+
+    vector<vector<int>> grid = {{0, 1, -1}, {1, 0, -1}, {1, 1, 1}};
+    cout << "actual: " << sol->cherryPickup(grid) << ", expected: " << 5 << endl;
+
+    grid = {{1, 1, -1}, {1, -1, 1}, {-1, 1, 1}};
+    cout << "actual: " << sol->cherryPickup(grid) << ", expected: " << 0 << endl;
+
+    return 0;
+}