Update 300_Longest_Increasing_Subsequence.java

Author: Sean Prashad

Dynamic Programming/300_Longest_Increasing_Subsequence.java

@@ -1,22 +1,33 @@
 class Solution {
     public int lengthOfLIS(int[] nums) {
-        if (nums == null || nums.length == 0) {
-            return 0;
+        int[] dp = new int[nums.length];
+        int len = 0;
+
+        for (int num : nums) {
+            int idx = binarySearch(dp, 0, len, num);
+            dp[idx] = num;
+
+            if (idx == len) {
+                ++len;
+            }
         }
 
-        int[] dp = new int[nums.length];
-        Arrays.fill(dp, 1);
-        int max = 1;
+        return len;
+    }
+
+    private int binarySearch(int[] nums, int low, int high, int target) {
+        while (low < high) {
+            int mid = low + (high - low) / 2;
 
-        for (int currNum = 0; currNum < nums.length; currNum++) {
-            for (int prevNum = 0; prevNum < currNum; prevNum++) {
-                if (nums[currNum] > nums[prevNum]) {
-                    dp[currNum] = Math.max(dp[currNum], dp[prevNum] + 1);
-                }
+            if (nums[mid] == target) {
+                return mid;
+            } else if (nums[mid] < target) {
+                low = mid + 1;
+            } else {
+                high = mid;
             }
-            max = Math.max(max, dp[currNum]);
         }
 
-        return max;
+        return low;
     }
 }