We have two integer sequences A
and B
of the same non-zero length.
We are allowed to swap elements A[i]
and B[i]
. Note that both elements are in the same index position in their respective sequences.
At the end of some number of swaps, A
and B
are both strictly increasing. (A sequence is strictly increasing if and only if A[0] < A[1] < A[2] < ... < A[A.length - 1]
.)
Given A and B, return the minimum number of swaps to make both sequences strictly increasing. It is guaranteed that the given input always makes it possible.
Example: Input: A = [1,3,5,4], B = [1,2,3,7] Output: 1 Explanation: Swap A[3] and B[3]. Then the sequences are: A = [1, 3, 5, 7] and B = [1, 2, 3, 4] which are both strictly increasing.
Note:
A, B
are arrays with the same length, and that length will be in the range[1, 1000]
.
A[i], B[i]
are integer values in the range[0, 2000]
.
题意:
给出两个相同长度的数组,求至少交换几次,使得两个数组都是严格递增的。交换必须是相同的index处交换,即A[i]只能与B[i]交换。
思路:
答案都看半天,手动再见,真难啊。。。还是找状态转移方程,设置数组dp[i][0]和dp[i][1],dp[i][0]表示第i处不交换需要交换的总次数,dp[i][1]表示第i次交换所需要交换的总次数。如果A[i-1]<A[i]&&B[i-1]<B[i],那么第i处不交换的话,dp[i][[0=min(dp[i][0],dp[i-1][0]),交换的话,dp[i][1]=min(dp[i-1][1]+1,dp[i][1]),因为交换第i处,那么第i-1处也可能也要交换。
对于A[i-1]<B[i]&&B[i-1]<A[i],也可以照此分析。
代码:
class Solution {
public int minSwap(int[] A, int[] B) {
int [][]dp=new int[A.length][2];
for(int i=0;i<A.length;i++)
{
dp[i][0]=Integer.MAX_VALUE;
dp[i][1]=Integer.MAX_VALUE;
}
dp[0][0]=0;
dp[0][1]=1;
for(int i=1;i<A.length;i++)
{
if(A[i-1]<A[i]&&B[i-1]<B[i])
dp[i][0]=Math.min(dp[i][0],dp[i-1][0]);
if(A[i-1]<B[i]&&B[i-1]<A[i])
dp[i][0]=Math.min(dp[i][0],dp[i-1][1]);
if(A[i-1]<A[i]&&B[i-1]<B[i])
dp[i][1]=Math.min(dp[i-1][1]+1,dp[i][1]);
if(A[i-1]<B[i]&&B[i-1]<A[i])
dp[i][1]=Math.min(dp[i][1],dp[i-1][0]+1);
}
return Math.min(dp[A.length-1][0],dp[A.length-1][1]);
}
}