Merge pull request chihungyu1116#10 from ignacio-chiazzo/closest-sum

3 Sum closest

Author: chihungyu1116

16 3Sum Closest.js

@@ -7,7 +7,7 @@ var threeSumClosest = function(nums, target) {
     if(nums === null || nums.length < 2){
         return null;
     }
-    
+
     if(nums.length === 3){
         return nums.reduce(function(prev,cur){return prev + cur;});
     }
@@ -16,34 +16,64 @@ var threeSumClosest = function(nums, target) {
     var closest = Infinity;
 
     nums.sort(function(a,b){return a > b ? 1 : -1;});
-    
+
     for(var i = 0; i < nums.length; i++){
         var j = i + 1;
         var k = nums.length - 1;
         while(j < k){
             var sum = nums[j] + nums[k] + nums[i];
             var diff = sum - target;
-            
+
             if(diff === 0){
                 return sum;
             }
-            
+
             if(sum < target){
                 diff = target - sum;
                 j++;
             } else {
                 diff = sum - target;
                 k--
             }
-            
+
             if(diff < closest){
                 closest = diff;
                 result = sum;
             }
         }
-        
+
         while(i < (nums.length-1) && nums[i] === nums[i+1]) i++;
     }
-    
+
     return result;
-};
+};
+
+//Shorter solution
+var threeSumClosest = function(nums, target) {
+    var closest = Number.Infinity;
+    var gap = -1;
+
+    nums.sort(function(a, b) { return a - b });
+    for(var i = 0; i < nums.length - 2; i++) {
+        var low = i + 1;
+        var high = nums.length - 1;
+
+        while(low < high) {
+            var sum = nums[i] + nums[low] + nums[high];
+            partialGap = Math.abs(target - sum);
+            if(partialGap < gap || gap === -1) {
+                gap = partialGap;
+                closest = sum;
+            }
+
+            if(sum === target) {
+                return target;
+            } else if (sum < target) {
+                low++;
+            } else {
+                high--;
+            }
+        }
+    }
+    return closest;
+};

18. 4Sum.js

@@ -0,0 +1,41 @@
+/**
+ * @param {number[]} nums
+ * @param {number} target
+ * @return {number[][]}
+ */
+var fourSum = function(nums, target) {
+    var results = [];
+    nums.sort(function(a,b) { return a - b });
+    for(var i = 0; i < nums.length - 3; i++) {
+        while(i > 0 && i < nums.length - 3 && nums[i] === nums[i - 1]) {
+            i++;
+        }
+        for(var j = i + 1; j < nums.length - 2; j++) {
+            while(j > i + 1 && j < nums.length - 2 && nums[j] === nums[j - 1]) {
+                j++;
+            }
+            var low = j + 1;
+            var high = nums.length - 1;
+            var newTarget = target - (nums[i] + nums[j]);
+            while(low < high) {
+                partialSum = nums[low] + nums[high];
+                if(partialSum === newTarget) {
+                    results.push([nums[i], nums[j], nums[low], nums[high]]);
+                    high--;
+                    low++;
+                    while(low < high && nums[low] === nums[low - 1]) {
+                        low++;
+                    }
+                    while(low < high && nums[high] === nums[high + 1]) {
+                        high--;
+                    }
+                } else if (partialSum > newTarget) {
+                    high--;
+                } else {
+                    low++;
+                }
+            }
+        }
+    }
+    return results;
+};

532. K-diff Pairs in an Array.js

@@ -0,0 +1,24 @@
+var findPairs = function(nums, k) {
+  if(nums.length === 0 || k < 0) {
+    return 0;
+  }
+  var dict = {};
+  var count = 0;
+
+  nums.sort(function(a,b){ return a - b });
+  for(var i = 0; i < nums.length; i++) {
+    var number = nums[i];
+    dict[number] = (dict[number] === undefined)? 1 : dict[number] += dict[number];
+  }
+  for(var numb in dict) {
+    numb = parseInt(numb);
+    if(k === 0) {
+      if(dict[numb] > 1) {
+        count++;
+      }
+    } else if(dict[numb + k] !== undefined){
+      count++;
+    }
+  }
+  return count;
+};