revisit some questions

Author: jyxia

Easy/160-IntersectionofTwoLinkedLists.js

@@ -44,3 +44,67 @@ var getLength = function(listHead) {
     }
     return length;
 };
+
+// 2nd try without knowing the length
+var getIntersectionNode = function(headA, headB) {
+    var intersection = null;
+    var pa = headA;
+    var pb = headB;
+
+    if (!pa || !pb) {
+        return intersection;
+    }
+
+    while (pa || pb) {
+        if (pa && pb && pa.val === pb.val) {
+            intersection = pa;
+        }
+
+        // this can be replace by pa === pb
+        while (pa && pb && pa.val === pb.val) {
+            pa = pa.next;
+            pb = pb.next;
+        }
+
+        if (pa === null && pb === null) {
+            break;
+        } else if (pa === null) {
+            pa = headB;
+        } else if (pb === null) {
+            pb = headA;
+        } else {
+            pa = pa.next;
+            pb = pb.next;
+        }
+    }
+
+    return intersection;
+};
+
+// more concise version,  compared to version 2
+var getIntersectionNode = function(headA, headB) {
+    var pa = headA;
+    var pb = headB;
+
+    if (!pa || !pb) {
+        return null;
+    }
+
+    while (pa && pb && pa !== pb) {
+        pa = pa.next;
+        pb = pb.next;
+        if (pa === pb) {
+           return pa ;
+        }
+
+        if (!pa) {
+            pa = headB;
+        }
+
+        if (!pb) {
+            pb = headA;
+        }
+    }
+
+    return pa;
+};

Medium/152-MaxProductSubarray.js

@@ -21,3 +21,18 @@ var maxProduct = function(nums) {
 
     return result;
 };
+
+// 2nd try
+var maxProduct = function(nums) {
+    var min = [nums[0]];
+    var max = [nums[0]];
+    var maxProduct = nums[0];
+
+    for (var i = 1; i < nums.length; i++) {
+        min.push(Math.min(nums[i], min[i - 1] * nums[i], max[i - 1] * nums[i]));
+        max.push(Math.max(nums[i], min[i - 1] * nums[i], max[i - 1] * nums[i]));
+        maxProduct = Math.max(maxProduct, max[i]);
+    }
+
+    return maxProduct;
+};

Medium/39-combinationSum.js

@@ -6,11 +6,12 @@
  * @return {number[][]}
  */
 var combinationSum = function(candidates, target) {
+    var result = [];
+    var results = [];
+    
     candidates.sort(function(a, b) {
       return a - b;
     });
-    var result = [];
-    var results = [];
     combinationSumHelper(candidates, target, results, result, 0);
     return results;
 };

Medium/40-combinationSumII.js

@@ -4,18 +4,19 @@
  * @return {number[][]}
  */
 var combinationSum2 = function(candidates, target) {
+    var result = [];
+    var results = [];
+
     candidates.sort(function(a, b) {
         return a - b;
     });
-    var result = [];
-    var results = [];
     combinationSum2Helper(candidates, result, results, target, 0);
     return results;
 };
 
 var combinationSum2Helper = function(candidates, result, results, target, start) {
   if (target === 0) {
-      results.push(deepCopy(result.slice()));
+      results.push(result.slice());
       return;
   }
 

Medium/50-powerxn.js

@@ -6,8 +6,21 @@
 var myPow = function(x, n) {
   if (n === 0) return 1;
   if (n < 0) {
-    n = -1 * n;
+    n *= -1;
     x = 1 / x;
   }
   return n % 2 === 0 ? myPow(x*x, n / 2) : x * myPow(x * x, Math.floor(n / 2));
 };
+
+// runtime error?
+var myPow = function(x, n) {
+    if (n === 0) {
+        return 1;
+    }
+
+    if (n === 1) {
+        return x;
+    }
+
+    return n > 0 ? myPow(x, n - 1) * x : x / myPow(x, -n - 1) * x;
+};