Solutions added for LeetCode 304, 881, 1376

Author: rayworks

src/main/java/org/sean/array/BoatCounter.java

@@ -0,0 +1,40 @@
+package org.sean.array;
+
+import java.util.Arrays;
+
+/***
+ * 881. Boats to Save People
+ */
+public class BoatCounter {
+    public int numRescueBoats(int[] people, int limit) {
+        // 2 pointers
+        Arrays.sort(people);
+
+        int len = people.length;
+        int left = 0, right = len - 1;
+        int cnt = 0;
+
+        while (left < right) {
+            int l = people[left];
+            int r = people[right];
+
+            if (r >= limit) {
+                right--;
+                cnt++;
+            } else {
+                if (l + r <= limit) {
+                    right--;
+                    left++;
+                    cnt++;
+                } else { // >
+                    right--;
+                    cnt++;
+                }
+            }
+        }
+        if (left == right)
+            cnt++;
+
+        return cnt;
+    }
+}

src/main/java/org/sean/array/NumMatrix.java

@@ -0,0 +1,43 @@
+package org.sean.array;
+
+/***
+ * 304. Range Sum Query 2D - Immutable
+ */
+public class NumMatrix {
+    private int[][] sumCache;
+
+    public NumMatrix(int[][] matrix) {
+        int rowCnt = matrix.length;
+        int colCnt = matrix[0].length;
+        sumCache = new int[rowCnt][colCnt];
+
+        for (int i = 0; i < rowCnt; i++) {
+            sumCache[i][0] = (i > 0 ? sumCache[i - 1][0] : 0) + matrix[i][0];
+        }
+
+        for (int j = 0; j < colCnt; j++) {
+            sumCache[0][j] = (j > 0 ? sumCache[0][j - 1] : 0) + matrix[0][j];
+        }
+
+        for (int i = 1; i < rowCnt; i++) {
+            for (int j = 1; j < colCnt; j++) {
+                sumCache[i][j] = sumCache[i - 1][j] + sumCache[i][j - 1] + matrix[i][j] - sumCache[i - 1][j - 1];
+            }
+        }
+    }
+
+    public int sumRegion(int row1, int col1, int row2, int col2) {
+        // 0 <= row1 <= row2 < m
+        int res = sumCache[row2][col2];
+        if (row1 > 0) {
+            res -= sumCache[row1 - 1][col2];
+        }
+        if (col1 > 0) {
+            res -= sumCache[row2][col1 - 1];
+        }
+        if (row1 > 0 && col1 > 0) {
+            res += sumCache[row1 - 1][col1 - 1];
+        }
+        return res;
+    }
+}

src/main/java/org/sean/tree/InformTime.java

@@ -0,0 +1,44 @@
+package org.sean.tree;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/***
+ * 1376. Time Needed to Inform All Employees
+ */
+public class InformTime {
+    private int timeCost;
+
+    private void numOfMinutesHelper(int pos, List<List<Integer>> g, int[] informTime, int sumSoFar) {
+        if (g.get(pos).isEmpty()) {
+            timeCost = Math.max(timeCost, sumSoFar);
+            return;
+        }
+
+        for (int e : g.get(pos)) {
+            numOfMinutesHelper(e, g, informTime, sumSoFar + informTime[e]);
+        }
+    }
+
+    public int numOfMinutes(int n, int headID, int[] manager, int[] informTime) {
+        // DFS max sum from root to leaf
+        if (n == 1)
+            return 0;
+
+        List<List<Integer>> graph = new ArrayList<>();
+        for (int i = 0; i < n; i++) {
+            graph.add(new ArrayList<>());
+        }
+
+        for (int j = 0; j < manager.length; j++) {
+            int mgr = manager[j];
+            if (mgr != -1) {
+                graph.get(mgr).add(j);
+            }
+        }
+
+        numOfMinutesHelper(headID, graph, informTime, informTime[headID]);
+
+        return timeCost;
+    }
+}

src/test/java/org/sean/array/BoatCounterTest.java

@@ -0,0 +1,21 @@
+package org.sean.array;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class BoatCounterTest {
+
+    private BoatCounter counter;
+
+    @Before
+    public void setUp() throws Exception {
+        counter = new BoatCounter();
+    }
+
+    @Test
+    public void numRescueBoats() {
+        assertEquals(2, counter.numRescueBoats(new int[]{5, 1, 4, 2}, 6));
+    }
+}

src/test/java/org/sean/array/NumMatrixTest.java

@@ -0,0 +1,29 @@
+package org.sean.array;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class NumMatrixTest {
+
+    private NumMatrix matrix;
+
+    @Before
+    public void setUp() throws Exception {
+        matrix = new NumMatrix(new int[][]{
+                new int[]{3, 0, 1, 4, 2},
+                new int[]{5, 6, 3, 2, 1},
+                new int[]{1, 2, 0, 1, 5},
+                new int[]{4, 1, 0, 1, 7},
+                new int[]{1, 0, 3, 0, 5}
+        });
+    }
+
+    @Test
+    public void sumRegion() {
+        assertEquals(8, matrix.sumRegion(2, 1, 4, 3));
+        assertEquals(11, matrix.sumRegion(1, 1, 2, 2));
+        assertEquals(12, matrix.sumRegion(1, 2, 2, 4));
+    }
+}

src/test/java/org/sean/tree/InformTimeTest.java

@@ -0,0 +1,24 @@
+package org.sean.tree;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class InformTimeTest {
+
+    private InformTime informTime;
+
+    @Before
+    public void setUp() throws Exception {
+        informTime = new InformTime();
+    }
+
+    @Test
+    public void numOfMinutes() {
+        int minutes = informTime.numOfMinutes(11, 4, new int[]{5, 9, 6, 10, -1, 8, 9, 1, 9, 3, 4},
+                new int[]{0, 213, 0, 253, 686, 170, 975, 0, 261, 309, 337});
+
+        assertEquals(2560, minutes);
+    }
+}