Count sum path solution

Tushar Roy · Tushar Roy · commit fa5f45bb5a06 · 2018-07-03T23:43:28.000-07:00
diff --git a/src/com/interview/tree/CountPathSum.java b/src/com/interview/tree/CountPathSum.java
@@ -0,0 +1,29 @@
+package com.interview.tree;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * https://leetcode.com/problems/path-sum-iii/description/
+ */
+public class CountPathSum {
+    public int pathSum(Node root, int sum) {
+        Map<Integer, Integer> map = new HashMap<>();
+        map.put(0, 1);
+        return countPathSum(root, sum, map, 0);
+    }
+
+    private int countPathSum(Node root, int sum, Map<Integer, Integer> map, int prefixSum) {
+        if (root == null) {
+            return 0;
+        }
+
+        prefixSum += root.data;
+        int count = map.getOrDefault(prefixSum - sum,0);
+        map.put(prefixSum, map.getOrDefault(prefixSum, 0) + 1);
+        count += countPathSum(root.left, sum, map, prefixSum) + countPathSum(root.right, sum, map, prefixSum);
+        map.put(prefixSum, map.getOrDefault(prefixSum, 1) - 1);
+        return count;
+    }
+}
+
