longest path with hurdel

Author: okmd

backtracking/lb-16-longest-path-with-hurdel.cpp

@@ -0,0 +1,43 @@
+#include<iostream>
+#include<vector>
+#include<limits.h>
+using namespace std;
+int dx[] = { 1,-1,0,0 };
+int dy[] = { 0,0,1,-1 };
+bool valid(vector<vector<int>>& mat, int i, int j) {
+    int n = mat.size();
+    int m = mat[0].size();
+    return (i < n and j < m and i >= 0 and j >= 0 and mat[i][j] == 1);
+}
+pair<int, int> findLongestPath(vector<vector<int>>& mat, int i, int j, int x, int y) {
+    if (i == x and j == y) return { true, 0 }; // found with length 0
+    if (!valid(mat, i, j)) return { false, INT_MAX };
+
+    int ans = INT_MIN;
+    
+    mat[i][j] = -1;
+    for (int k = 0; k < 4; k++) {
+        int p = i + dx[k], q = j + dy[k];
+        auto [found, length] = findLongestPath(mat, p, q, x, y);
+        if (found) ans = max(ans, length);
+    }
+    mat[i][j] = 1; // as 0 or -1 will not be visited again
+    if (ans == INT_MIN) return { false, INT_MAX };
+    return { true, 1 + ans };
+}
+int main() {
+    // input matrix with hurdles shown with number 0
+    vector<vector<int>> mat = {
+        { 1, 1, 1, 1, 1, 1, 1, 1, 1, 1 },
+        { 1, 1, 0, 1, 1, 0, 1, 1, 0, 1 },
+        { 1, 1, 1, 1, 1, 1, 1, 1, 1, 1 }
+    };
+    // find longest path with source (0, 0) and
+    // destination (1, 7)
+    int i = 0, j = 0;
+    int x = 1, y = 7;
+    auto [found, length] = findLongestPath(mat, i, j, x, y);
+    cout << (found ? to_string(length) : "Not found\n");
+    return 0;
+}
+// https://leetcode.com/playground/39yreovk