Create minimum-array-changes-to-make-differences-equal.py

Author: kamyu104

Python/minimum-array-changes-to-make-differences-equal.py

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+# Time:  O(n + k)
+# Space: O(k)
+
+# prefix sum, difference array
+class Solution(object):
+    def minChanges(self, nums, k):
+        """
+        :type nums: List[int]
+        :type k: int
+        :rtype: int
+        """
+        diff = [0]*((k+1)+1)
+        def update(left, right, d):
+            diff[left] += d
+            diff[right+1] -= d
+
+        for i in xrange(len(nums)//2):
+            curr = abs(nums[i]-nums[~i])
+            mx = max(nums[i]-0, k-nums[i], nums[~i]-0, k-nums[~i])
+            # 1 change for i in range(0, curr)
+            update(0, curr-1, 1)
+            # 1 change for i in range(curr+1, mx+1)
+            update(curr+1, mx, 1)
+            # 2 changes for i in range(mx+1, k+1)
+            update(mx+1, k, 2)
+        result = len(nums)//2
+        curr = 0
+        for i in xrange(k+1):
+            curr += diff[i]
+            result = min(result, curr)
+        return result