Update 1143, 252, 42

java/1143-Longest-Common-Subsequence.java

@@ -19,3 +19,39 @@ public int LCS(String s1, String s2, int i, int j, int[][] dp) {
         }
     }
 }
+
+
+// Iterative version
+class Solution {
+    public int longestCommonSubsequence(String text1, String text2) {
+        //O(n*m)/O(n*m)  time/memory
+        if (text1.isEmpty() || text2.isEmpty()) {
+            return 0;
+        }
+
+        int[][] dp = new int[text1.length() + 1][text2.length() + 1];
+
+        for (int i = 0; i <= text1.length(); i++) {
+            dp[i][0] = 0;
+        }
+
+        for (int j = 0; j <= text2.length(); j++) {
+            dp[0][j] = 0;
+        }
+
+        for (int i = 1; i <= text1.length(); i++) {
+            for (int j = 1; j <= text2.length(); j++) {
+                if (text1.charAt(i - 1) == text2.charAt(j - 1)) {
+                    dp[i][j] = 1 + dp[i - 1][j - 1];
+
+                } else {
+                    dp[i][j] = Math.max(dp[i][j - 1], dp[i - 1][j]);
+                }
+
+            }
+        }
+
+        return dp[text1.length()][text2.length()];
+    }
+}
+

java/252-Meeting-Rooms.java

@@ -39,3 +39,18 @@ public boolean canAttendMeetings(List<Interval> intervals) {
         return true;
     }
 }
+
+
+public class Solution {
+    public boolean canAttendMeetings(List<Interval> intervals) {
+
+       Collections.sort(intervals, (a, b) -> a.start - b.start);
+
+       for(int i=0; i+1 < intervals.size(); i++){
+           if(intervals.get(i).end > intervals.get(i+1).start){
+               return false;
+           }
+       }
+       return true;
+    }
+}

java/253-Meeting-Rooms-ii.java

@@ -39,3 +39,42 @@ public int minMeetingRooms(List<Interval> intervals) {
         return count;
     }
 }
+
+// Two pointer approach
+public class Solution {
+    public int minMeetingRooms(List<Interval> intervals) {
+        if (intervals.size() == 0) {
+            return 0;
+        }
+
+        int len = intervals.size();
+        int[] startTime = new int[len];
+        int[] endTime = new int[len];
+
+        for (int i = 0; i < len; i++) {
+            startTime[i] = intervals.get(i).start;
+            endTime[i] = intervals.get(i).end;
+        }
+
+        Arrays.sort(startTime);
+        Arrays.sort(endTime);
+
+        int res = 0;
+        int count = 0;
+        int s = 0;
+        int e = 0;
+
+        while (s < len) {
+            if (startTime[s] < endTime[e]) {
+                s++;
+                count++;
+            } else {
+                e++;
+                count--;
+            }
+            res = Math.max(res, count);
+        }
+
+        return res;
+    }
+}

java/42-Trapping-Rain-Water.java

@@ -21,3 +21,30 @@ public int trap(int[] heights) {
         return c;
     }
 }
+
+//O(1) space
+class Solution {
+    public int trap(int[] heights) {
+
+        if (heights.length == 0) return 0;
+
+        int l = 0, r = heights.length - 1;
+        int leftMax = heights[l], rightMax = heights[r];
+        int res = 0;
+
+        while (l < r) {
+            if (leftMax < rightMax) {
+                l++;
+                leftMax = Math.max(leftMax, heights[l]);
+                res += leftMax - heights[l];
+            } else {
+                r--;
+                rightMax = Math.max(rightMax, heights[r]);
+                res += rightMax - heights[r];
+            }
+        }
+
+        return res;
+
+    }
+}