Add solution for 743 (fishercoder1534#51)

Author: havanagrawal

README.md

@@ -114,6 +114,7 @@ Your ideas/fixes/algorithms are more than welcome!
 |747|[Largest Number Greater Than Twice of Others](https://leetcode.com/problems/largest-number-greater-than-twice-of-others/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_747.java) | O(n) | O(1) | |Easy|
 |746|[Min Cost Climbing Stairs](https://leetcode.com/problems/min-cost-climbing-stairs/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_746.java) | O(n) | O(1) | |Easy|
 |744|[Find Smallest Letter Greater Than Target](https://leetcode.com/problems/find-smallest-letter-greater-than-target/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_744.java) | O(logn) | O(1) || Easy|
+|743|[Network Delay Time](https://leetcode.com/problems/network-delay-time/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_743.java) | O(n^2 + e) | O(n^2) || Medium|Graph, Djikstra|
 |740|[Delete and Earn](https://leetcode.com/problems/delete-and-earn/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_740.java) | O(n) | O(n) | |Medium|
 |739|[Daily Temperatures](https://leetcode.com/problems/daily-temperatures/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_739.java) | O(n^2) | O(1) | |Medium| 
 |738|[Monotone Increasing Digits](https://leetcode.com/problems/monotone-increasing-digits/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_738.java) | O(n) | O(1) | |Medium|

src/main/java/com/fishercoder/solutions/_743.java

@@ -0,0 +1,96 @@
+package com.fishercoder.solutions;
+
+/**
+ * 743. Network Delay Time
+ *
+ * There are N network nodes, labelled 1 to N.
+ *
+ *  Given times, a list of travel times as directed edges times[i] = (u, v, w), where u is the source node, v is the target node, and w is the time it takes for a signal to travel from source to target.
+ *
+ * Now, we send a signal from a certain node K. How long will it take for all nodes to receive the signal? If it is impossible, return -1.
+ *
+ * Note:
+ *  * N will be in the range [1, 100].
+ *  * K will be in the range [1, N].
+ *  * The length of times will be in the range [1, 6000].
+ *  * All edges times[i] = (u, v, w) will have 1 <= u, v <= N and 0 <= w <= 100.
+ */
+
+public class _743 {
+    public static class Solution1 {
+        public static final int MAX = 100_00_00;
+
+        private int[][] parseTimes(int[][] times, int N) {
+            int[][] weights = new int[N + 1][N + 1];
+
+            for (int i = 0; i < N + 1; ++i) {
+                for (int j = 0; j < N + 1; ++j) {
+                    weights[i][j] = MAX;
+                }
+            }
+
+            for (int[] time : times) {
+                int u = time[0];
+                int v = time[1];
+                int w = time[2];
+                weights[u][v] = w;
+            }
+
+            return weights;
+        }
+
+        private int findMinUnvisitedIndex(int[] a, boolean[] visited) {
+            int min = Integer.MAX_VALUE;
+            int minIdx = 1;
+
+            for (int i = 1; i < a.length; ++i) {
+                if (a[i] < min && !visited[i]) {
+                    min = a[i];
+                    minIdx = i;
+                }
+            }
+            return minIdx;
+        }
+
+        public int networkDelayTime(int[][] times, int N, int K) {
+            // Time from u to v is weights[u][v]
+            int[][] weights = parseTimes(times, N);
+
+            // Time from node K to note i is totalTime[i]
+            int[] totalTime = new int[N + 1];
+            for (int j = 0; j <= N; ++j) {
+                totalTime[j] = MAX;
+            }
+            totalTime[K] = 0;
+
+            boolean[] visited = new boolean[N + 1];
+            int visitCount = 0;
+
+            while (visitCount != N) {
+                int node = findMinUnvisitedIndex(totalTime, visited);
+
+                // The smallest time to a node is more than our designated max
+                // so it must be unreachable
+                if (totalTime[node] >= MAX) {
+                    return -1;
+                }
+
+                visited[node] = true;
+                visitCount += 1;
+
+                // Update the time to each node if we try to visit it from our current node
+                for (int i = 1; i <= N; ++i) {
+                    totalTime[i] = Math.min(weights[node][i] + totalTime[node], totalTime[i]);
+                }
+            }
+
+            // What is the maximum time to any particular node
+            int maxVal = Integer.MIN_VALUE;
+            for (int k = 1; k <= N; ++k) {
+                maxVal = Math.max(totalTime[k], maxVal);
+            }
+
+            return maxVal;
+        }
+    }
+}

src/test/java/com/fishercoder/_743Test.java

@@ -0,0 +1,28 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._743;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class _743Test {
+    private static _743.Solution1 solution1;
+
+    @BeforeClass
+    public static void setup() {
+        solution1 = new _743.Solution1();
+    }
+
+    @Test
+    public void test1() {
+        int[][] times = {{2, 1, 1}, {2, 3, 1}, {3, 4, 1}};
+        assertEquals(solution1.networkDelayTime(times, 4, 2), 2);
+    }
+
+    @Test
+    public void test2() {
+        int[][] times = {{2, 1, 1}, {2, 3, 1}, {3, 4, 1}};
+        assertEquals(solution1.networkDelayTime(times, 4, 3), -1);
+    }
+}