longest-consecutive-sequence

Author: chjung99

longest-consecutive-sequence/chjung99.java

@@ -0,0 +1,64 @@
+class Solution {
+    int[] dp;
+    int[] next;
+    int n;
+    Map<Integer, Integer> location;
+
+    public int longestConsecutive(int[] nums) {
+        n = nums.length;
+        dp = new int[n];
+        next = new int[n];
+        location = new HashMap<>();
+
+        for (int i = 0; i < n; i++){
+            location.put(nums[i], i);
+            dp[i] = -1;
+        }
+
+        for (int i = 0; i < n; i++){
+            int nextValue = nums[i] + 1;
+            if (location.containsKey(nextValue)) {
+                next[i] = location.get(nextValue);
+                continue;
+            }
+            next[i] = -1;
+        }
+
+        for (int i = 0; i < n; i++) {
+            if (next[i] == -1) {
+                dp[i] = 1;
+                continue;
+            }
+            if (dp[next[i]] == -1) {
+                dp[i] = 1 + find(next[i], nums);
+                continue;
+            }
+            if (dp[next[i]] != -1){
+                dp[i] = 1 + dp[next[i]];
+            }
+        }
+        int answer = 0;
+        for (int i = 0; i < n; i++){
+            // System.out.print(dp[i] + " ");
+            answer = Math.max(answer, dp[i]);
+        }
+        return answer;
+    }
+
+    public int find(int idx, int[] nums) {
+        if (next[idx] == -1) {
+            dp[idx] = 1;
+        }
+        else if (dp[next[idx]] == -1) {
+            dp[idx] = 1 + find(next[idx], nums);
+        }
+        else if (dp[next[idx]] != -1) {
+            dp[idx] = 1 + dp[next[idx]];
+        }
+        return dp[idx];
+    }
+
+
+}
+
+