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MinimumNumberOfPartitions.java
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MinimumNumberOfPartitions.java
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/*https://leetcode.com/problems/palindrome-partitioning-ii/*/
class Solution
{
int[][] dp;
public boolean isPalindrome(String str, int start, int end)
{
while(start<end)
{
if(str.charAt(start)!=str.charAt(end))
return false;
start++;
end--;
}
return true;
}
public int palindromicPartitionSolver(String s, int start, int end)
{
//base case
if(start >= end) return 0;
//if already calculated, return
if(dp[start][end] != -1) return dp[start][end];
/*If the current string is palindrome then we dont need to break it into
further sub problems as we want to minimize the cuts.*/
if(isPalindrome(s, start, end))
{
dp[start][end]=0;
return 0;
}
int min = Integer.MAX_VALUE;
//trying Different possible cuts between i and j
for (int k = start; k <= end; ++k)
{
//if start to k substring is palindrome, then we shall recur for k+1 to end
if (isPalindrome(s, start, k))
{
int partitions = 1+palindromicPartitionSolver(s, k+1, end);
min = Math.min(min, partitions);
}
}
//store answer in table and return
dp[start][end] = min;
return dp[start][end];
}
public int minCut(String s)
{
dp = new int[s.length()][s.length()];
//fill the table with -1
for (int i = 0; i < dp.length; ++i)
for (int j = 0; j < dp[0].length; ++j)
dp[i][j] = -1;
return palindromicPartitionSolver(s, 0, s.length()-1);
}
}
class Solution {
int minCuts;
Integer[] ccm;
public int minCut(String s) {
minCuts = Integer.MAX_VALUE;
if (s.length() == 0) return 1;
ccm = new Integer[s.length()+1];
recur(s,0,s.length(),0);
return minCuts-1;
}
public int recur(String s, int index, int n, int cutsCount)
{
if (index == n)
{
if (cutsCount < minCuts) minCuts = cutsCount;
ccm[index] = 0;
return 0;
}
int result = Integer.MAX_VALUE;
if (ccm[index] != null) return ccm[index];
for (int i = index; i < n; ++i)
{
if (isPalindrome(s.substring(index,i+1)))
result = Math.min(result,recur(s, i+1, n, cutsCount+1)+1);
}
ccm[index] = result;
if (cutsCount+ccm[index] < minCuts) minCuts = cutsCount+ccm[index];
return ccm[index];
}
public boolean isPalindrome(String s)
{
int i = 0, j = s.length()-1;
while (i < j)
{
if (s.charAt(i) != s.charAt(j)) return false;
++i;
--j;
}
return true;
}
}
//best solution
class Solution {
public int minCut(String s) {
//1D Space expand around middle
char[] a = s.toCharArray();
int n = a.length;
int[] dp = new int[n];
for(int i = 0;i<n;i++) dp[i] = i;
for(int i = 0;i<n;i++)
{
solve(a,dp,i,i);
solve(a,dp,i,i+1);
}
return dp[n-1];
}
public void solve(char[] s,int[] dp, int l, int r)
{
int n = s.length;
while(l >= 0 && r < n && s[l] == s[r])
{
if(l == 0)
dp[r] = 0;
else
dp[r] = Math.min(1 + dp[l-1],dp[r]);
l--;
r++;
}
}
}
public class Solution {
public int minCut(String s) {
int n = s.length();
char[] t = s.toCharArray();
int[] dp = new int[n + 1];
Arrays.fill(dp, Integer.MAX_VALUE);
dp[0] = -1;
int i = 0;
while (i < n) {
expandAround(t, i, i, dp);
expandAround(t, i, i + 1, dp);
i++;
}
return dp[n];
}
private void expandAround(char[] t, int i, int j, int[] dp) {
while (i >= 0 && j < t.length && t[i] == t[j]) {
dp[j + 1] = Math.min(dp[j + 1], dp[i] + 1);
i--;
j++;
}
}
}