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Problem solution · Java

Minimum Distance to Type a Word Using Two Fingers

Minimum Distance to Type a Word Using Two Fingers: a Java solution using sliding window or two pointers. Learn the idea, check the complexity, and read the full code, with credit to walkccc LeetCode Solutions.

Technique
Sliding window or two pointers
Source
walkccc LeetCode Solutions
Length
31 lines
Start with the idea.

Try the problem first. If you get stuck, read the approach below, then write your own solution. The full code is at the bottom.

Approach

Sliding window or two pointers

For Minimum Distance to Type a Word Using Two Fingers, the implementation maintains a moving interval and updates only the information that enters or leaves the window.

  1. Choose the invariant that makes a window valid or useful.
  2. Advance the right boundary and add the new element.
  3. Move the left boundary only as needed while maintaining the invariant and updating the answer.

Code notes

  • 31 lines of Java from the credited upstream file 1320.java.
  • The implementation visibly relies on sequence storage.
  • No explicit loop blocks detected.

Complexity

Confirm that neither pointer moves backwards; if so, the scan is usually linear apart from the window’s data-structure operations.

Check the problem constraints before deciding whether this complexity will pass.

Source

Code and credit

This code comes from walkccc LeetCode Solutions by P.-Y. Chen (walkccc) and is used under the MIT licence.

Open problem ↗Original source ↗
Full codeMinimum Distance to Type a Word Using Two Fingers · JavaJava
Use this to learn the idea, then write your own version.
class Solution {  public int minimumDistance(String word) {    Integer[][][] mem = new Integer[27][27][word.length()];    return minimumDistance(word, 26, 26, 0, mem);  }   // Returns the minimum distance to type `word`, where the left finger is on  // the i-th letter, the right finger is on the j-th letter, and word[0..k)  // have been written.  private int minimumDistance(final String word, int i, int j, int k, Integer[][][] mem) {    if (k == word.length())      return 0;    if (mem[i][j][k] != null)      return mem[i][j][k];    final int c = word.charAt(k) - 'A';    final int moveLeft = dist(i, c) + minimumDistance(word, c, j, k + 1, mem);    final int moveRight = dist(j, c) + minimumDistance(word, i, c, k + 1, mem);    return mem[i][j][k] = Math.min(moveLeft, moveRight);  }   private int dist(int a, int b) {    if (a == 26) // the first hovering state      return 0;    final int x1 = a / 6;    final int y1 = a % 6;    final int x2 = b / 6;    final int y2 = b % 6;    return Math.abs(x1 - x2) + Math.abs(y1 - y2);  }}

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