[sora0319] WEEK 09 solutions

linked-list-cycle/sora0319.java

@@ -0,0 +1,20 @@
+public class sora0319 {
+    public class Solution {
+        public boolean hasCycle(ListNode head) {
+            ListNode back = head;
+            ListNode front = head;
+
+            while (front != null && front.next != null) {
+                back = back.next;
+                front = front.next.next;
+
+                if (back == front) {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+    }
+}
+

maximum-product-subarray/sora0319.java

@@ -0,0 +1,23 @@
+public class sora0319 {
+    public class Solution {
+        public int maxProduct(int[] nums) {
+            int result = nums[0];
+            int max = 1;
+            int min = 1;
+
+            for (int num : nums) {
+                int tempMax = Math.max(Math.max(max * num, min * num), num);
+                int tempMin = Math.min(Math.min(max * num, min * num), num);
+
+                max = tempMax;
+                min = tempMin;
+
+                result = Math.max(result, max);
+            }
+
+            return result;
+        }
+    }
+
+}
+

minimum-window-substring/sora0319.java

@@ -0,0 +1,87 @@
+public class sora0319 {
+    public class Solution {
+        public String minWindow(String s, String t) {
+            if (s.length() < t.length()) return "";
+
+            Map<Character, Integer> tCounts = new HashMap<>();
+            Map<Character, Integer> wCounts = new HashMap<>();
+
+            // tCounts 초기화
+            for (char ch : t.toCharArray()) {
+                if (tCounts.containsKey(ch)) {
+                    tCounts.put(ch, tCounts.get(ch) + 1);
+                } else {
+                    tCounts.put(ch, 1);
+                }
+            }
+
+            int minLow = 0;
+            int minHigh = s.length();
+            int low = 0;
+            boolean found = false;
+
+            for (int high = 0; high < s.length(); high++) {
+                char ch = s.charAt(high);
+                if (wCounts.containsKey(ch)) {
+                    wCounts.put(ch, wCounts.get(ch) + 1);
+                } else {
+                    wCounts.put(ch, 1);
+                }
+
+                while (isExist(wCounts, tCounts)) {
+                    if (high - low < minHigh - minLow) {
+                        minLow = low;
+                        minHigh = high;
+                        found = true;
+                    }
+
+                    char lowChar = s.charAt(low);
+                    if (tCounts.containsKey(lowChar)) {
+                        int count = wCounts.get(lowChar);
+                        if (count == 1) {
+                            wCounts.remove(lowChar);
+                        } else {
+                            wCounts.put(lowChar, count - 1);
+                        }
+                    } else {
+                        if (wCounts.containsKey(lowChar)) {
+                            int count = wCounts.get(lowChar);
+                            if (count == 1) {
+                                wCounts.remove(lowChar);
+                            } else {
+                                wCounts.put(lowChar, count - 1);
+                            }
+                        }
+                    }
+
+                    low++;
+                }
+            }
+
+            if (found) {
+                return s.substring(minLow, minHigh + 1);
+            } else {
+                return "";
+            }
+        }
+
+        private boolean isExist(Map<Character, Integer> window, Map<Character, Integer> target) {
+            for (Map.Entry<Character, Integer> entry : target.entrySet()) {
+                char ch = entry.getKey();
+                int required = entry.getValue();
+
+                if (!window.containsKey(ch)) {
+                    return false;
+                }
+
+                int count = window.get(ch);
+                if (count < required) {
+                    return false;
+                }
+            }
+            return true;
+        }
+    }
+}
+
+

pacific-atlantic-water-flow/sora0319.java

@@ -0,0 +1,67 @@
+public class sora0319 {
+    public class Solution {
+        private int[][] heights;
+        private int rows, cols;
+
+        public List<List<Integer>> pacificAtlantic(int[][] heights) {
+            this.heights = heights;
+            this.rows = heights.length;
+            this.cols = heights[0].length;
+            List<List<Integer>> result = new ArrayList<>();
+
+            for (int row = 0; row < rows; row++) {
+                for (int col = 0; col < cols; col++) {
+                    Set<String> visitedPac = new HashSet<>();
+                    Set<String> visitedAtl = new HashSet<>();
+
+                    if (dfsPac(row, col, visitedPac) && dfsAtl(row, col, visitedAtl)) {
+                        result.add(Arrays.asList(row, col));
+                    }
+                }
+            }
+            return result;
+        }
+
+        private boolean dfsPac(int row, int col, Set<String> visited) {
+            String key = row + "," + col;
+            if (visited.contains(key)) return false;
+            visited.add(key);
+
+            if (row == 0 || col == 0) return true;
+
+            int[][] moved = { {0, -1}, {0, 1}, {-1, 0}, {1, 0} };
+            for (int[] m : moved) {
+                int r = row + m[0];
+                int c = col + m[1];
+                if (isRange(r, c) && heights[row][col] >= heights[r][c]) {
+                    if (dfsPac(r, c, visited)) return true;
+                }
+            }
+            return false;
+        }
+
+        private boolean dfsAtl(int row, int col, Set<String> visited) {
+            String key = row + "," + col;
+            if (visited.contains(key)) return false;
+            visited.add(key);
+
+            if (row == rows - 1 || col == cols - 1) return true;
+
+            int[][] directions = { {0, -1}, {0, 1}, {-1, 0}, {1, 0} };
+            for (int[] dir : directions) {
+                int r = row + dir[0];
+                int c = col + dir[1];
+                if (isRange(r, c) && heights[row][col] >= heights[r][c]) {
+                    if (dfsAtl(r, c, visited)) return true;
+                }
+            }
+            return false;
+        }
+
+        private boolean isRange(int r, int c) {
+            return r >= 0 && r < rows && c >= 0 && c < cols;
+        }
+    }
+
+}
+

sum-of-two-integers/sora0319.java

@@ -0,0 +1,13 @@
+public class sora0319 {
+    class Solution {
+        public int getSum(int a, int b) {
+            while (b != 0) {
+                int carry = a & b;
+                a = a ^ b;
+                b = carry << 1;
+            }
+            return a;
+        }
+    }
+}
+