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Author: BaffinLee

201-300/283. Move Zeroes.md

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+# 283. Move Zeroes
+
+- Difficulty: Easy.
+- Related Topics: Array, Two Pointers.
+- Similar Questions: Remove Element.
+
+## Problem
+
+Given an array ```nums```, write a function to move all ```0```'s to the end of it while maintaining the relative order of the non-zero elements.
+
+**Example:**
+
+```
+Input: [0,1,0,3,12]
+Output: [1,3,12,0,0]
+```
+
+**Note**:
+
+
+	
+- You must do this **in-place** without making a copy of the array.
+	
+- Minimize the total number of operations.
+
+
+## Solution
+
+```javascript
+/**
+ * @param {number[]} nums
+ * @return {void} Do not return anything, modify nums in-place instead.
+ */
+var moveZeroes = function(nums) {
+  var len = nums.length;
+  var lastZeroIndex = -1;
+  for (var i = 0; i < len; i++) {
+    if (nums[i] === 0 && lastZeroIndex === -1) {
+      lastZeroIndex = i;
+    } else if (nums[i] !== 0 && lastZeroIndex !== -1) {
+      swap(nums, i, lastZeroIndex);
+      lastZeroIndex += 1;
+    }
+  }
+};
+
+var swap = function(arr, i, j) {
+  var tmp = arr[i];
+  arr[i] = arr[j];
+  arr[j] = tmp;
+};
+```
+
+**Explain:**
+
+two pointer: index in the loop and last zero index we met.
+
+every time we met a non-zero element, swap it with the last zero element, move the last zero element's index.
+
+every time we met a zero element, log it if we haven't met any zero yet, otherwise just move on and do nothing.
+
+**Complexity:**
+
+* Time complexity : O(n).
+* Space complexity : O(1).