From ee8def9d6b460ecb0a3b5ac31b386677a5af5c30 Mon Sep 17 00:00:00 2001
From: chunyang <chunyang.wen@gmail.com>
Date: Mon, 20 Jul 2020 07:04:46 +0800
Subject: [PATCH] add minmum steps to reach

---
 minimum-steps-to-reach.cpp | 79 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)
 create mode 100644 minimum-steps-to-reach.cpp

diff --git a/minimum-steps-to-reach.cpp b/minimum-steps-to-reach.cpp
new file mode 100644
index 0000000..cefef04
--- /dev/null
+++ b/minimum-steps-to-reach.cpp
@@ -0,0 +1,79 @@
+#include <iostream>
+#include <vector>
+#include <set>
+
+using namespace std;
+
+typedef pair<int, int> Pos;
+
+
+int minimum_steps(const vector<vector<bool>>& m, pair<int, int> s, pair<int, int> e) {
+
+    int row = m.size();
+    int col = m[0].size();
+    vector<vector<int>> distance(row, vector<int>(col, -1));
+    distance[s.first][s.second] = 0;
+    vector<Pos> st;
+    vector<Pos> next_st;
+    int step = 1;
+    st.push_back(s);
+    int limit = row * col;
+    while (distance[e.first][e.second] == -1 && step < limit) {
+
+        while (!st.empty()) {
+            auto b = st.back(); st.pop_back();
+
+            // right
+            Pos p  = make_pair(b.first, b.second+1);
+            if (p.second < col && !m[p.first][p.second]) {
+                if (distance[p.first][p.second] == -1) {
+                    distance[p.first][p.second] = step;
+                    next_st.push_back(p);
+                }
+            }
+
+            // left
+            p  = make_pair(b.first, b.second-1);
+            if (p.second >= 0 && !m[p.first][p.second]) {
+                if (distance[p.first][p.second] == -1) {
+                    distance[p.first][p.second] = step;
+                    next_st.push_back(p);
+                }
+            }
+
+
+            // top
+            p  = make_pair(b.first-1, b.second);
+            if (p.first >= 0 && !m[p.first][p.second]) {
+                if (distance[p.first][p.second] == -1) {
+                    distance[p.first][p.second] = step;
+                    next_st.push_back(p);
+                }
+            }
+
+            // bottom
+            p  = make_pair(b.first+1, b.second);
+            if (p.first < row && !m[p.first][p.second]) {
+                if (distance[p.first][p.second] == -1) {
+                    distance[p.first][p.second] = step;
+                    next_st.push_back(p);
+                }
+            }
+        }
+        st.swap(next_st);
+        ++step;
+    }
+
+    return distance[e.first][e.second];
+}
+
+int main() {
+    vector<vector<bool>> m{
+        {false, false, false, false},
+        {true, true, false, true},
+        {false, false, false, false},
+        {false, false, false, false}
+    };
+    cout << minimum_steps(m, {3 ,0}, {0, 0}) << endl;
+    return 0;
+}