update 523 java

Author: yennanliu

leetcode_java/src/main/java/LeetCodeJava/HashTable/ContinuousSubarraySum.java

@@ -76,6 +76,10 @@ public boolean checkSubarraySum(int[] nums, int k) {
             presum += nums[i];
 
             // Calculate remainder
+            /**
+             * NOTE:
+             *  handle edge case : if k = 0
+             */
             int remainder = (k != 0) ? presum % k : presum;
 
             // If the remainder already exists in the map
@@ -158,6 +162,37 @@ public boolean checkSubarraySum_0_1(int[] nums, int k) {
         return false;
     }
 
+    // V0-2
+    // IDEA : presum + hashmap
+    public boolean checkSubarraySum_0_2(int[] nums, int k) {
+
+        if (nums.length < 2) {
+            return false;
+        }
+
+        Map<Integer, Integer> map = new HashMap<>();
+        // NOTE!! init as below
+        map.put(0, -1);
+
+        int preSum = 0;
+        for (int i = 0; i < nums.length; i++) {
+            int cur = nums[i];
+            /**
+             * NOTE:
+             *  handle edge case : if k = 0
+             */
+            preSum = k != 0 ? (preSum + cur) % k : preSum;
+            if (map.containsKey(preSum)) {
+                if (i - map.get(preSum) >= 2) {
+                    return true;
+                }
+            } else {
+                map.put(preSum, i);
+            }
+        }
+        return false;
+    }
+
 
     // V1
     // IDEA : HASHMAP

leetcode_java/src/main/java/dev/workspace6.java

@@ -320,4 +320,44 @@ private Integer[] createPreSumArr(int[] input, int n){
       return res;
     }
 
+    // LC 523
+    // https://leetcode.com/problems/continuous-subarray-sum/
+    // 3.11 pm - 3.20 pm
+    /**
+     *  idea : presum + hashmap
+     *
+     */
+    public boolean checkSubarraySum(int[] nums, int k) {
+
+      if (nums.length < 2){
+          return false;
+      }
+
+      Map<Integer, Integer> map = new HashMap<>();
+      // NOTE!! init as below
+      map.put(0, -1);
+
+      int preSum = 0;
+      for(int i = 0; i < nums.length; i++){
+          int cur = nums[i];
+          //  int remainder = (k != 0) ? presum % k : presum;
+          preSum = k != 0 ? (preSum + cur) % k : preSum; // edge case : if k = 0
+          /**
+           *  sum(i,j) = presum(j+1) - presum(i)
+           *
+           *  -> sum(i,j) = a * k + r  - b * k + r
+           *  ->
+           *
+           */
+          if (map.containsKey(preSum)){ // TODO : double check
+              if (i - map.get(preSum) >= 2){
+                  return true;
+              }
+          }
+          map.put(preSum, i);
+      }
+
+      return false;
+    }
+
 }