Runtime: 70 ms (Top 80.89%) | Memory: 47.60 MB (Top 75.77%)

Author: AnasImloul

scripts/algorithms/P/Path Sum III/Path Sum III.js

@@ -1,27 +1,11 @@
-var pathSum = function(root, targetSum) {
-let count = 0;
-
-let hasSum = (node, target) => { //helper function, calculates number of paths having sum equal to target starting from given node
-    if(node===null){// base case
-        return;
-    }
-    if(node.val===target){// if at any point path sum meets the requirement
-        count++;
-    }
-    //recursive call
-    hasSum(node.left, target-node.val);
-    hasSum(node.right, target-node.val);
-}
-
-let dfs = (node) => {//dfs on every node and find sum equal to target starting from every node
-    if(node===null)
-        return;
-    dfs(node.left);
-    dfs(node.right);
-    hasSum(node,targetSum);// find sum of path starting on this point
-}
-
-dfs(root);
-
-return count;
-};
+// Runtime: 70 ms (Top 80.89%) | Memory: 47.60 MB (Top 75.77%)
+
+var pathSum = function(root, sum, presums = { '0': 1 }, prev = 0) {
+    if (!root) return 0;
+    let curr = prev + root.val;
+    presums[curr] = (presums[curr] || 0) + 1;
+    let res = (presums[curr - sum] || 0) - !sum;
+    res += pathSum(root.left, sum, presums, curr) + pathSum(root.right, sum, presums, curr);
+    presums[curr]--;
+    return res;
+};