FlippingAnImage832.java

/**
 * Given a binary matrix A, we want to flip the image horizontally, then invert
 * it, and return the resulting image.
 * 
 * To flip an image horizontally means that each row of the image is reversed.
 * For example, flipping [1, 1, 0] horizontally results in [0, 1, 1].
 * 
 * To invert an image means that each 0 is replaced by 1, and each 1 is
 * replaced by 0. For example, inverting [0, 1, 1] results in [1, 0, 0].
 * 
 * Example 1:
 * Input: [[1,1,0],[1,0,1],[0,0,0]]
 * Output: [[1,0,0],[0,1,0],[1,1,1]]
 * Explanation: First reverse each row: [[0,1,1],[1,0,1],[0,0,0]].
 * Then, invert the image: [[1,0,0],[0,1,0],[1,1,1]]
 * 
 * Example 2:
 * Input: [[1,1,0,0],[1,0,0,1],[0,1,1,1],[1,0,1,0]]
 * Output: [[1,1,0,0],[0,1,1,0],[0,0,0,1],[1,0,1,0]]
 * Explanation: First reverse each row: [[0,0,1,1],[1,0,0,1],[1,1,1,0],[0,1,0,1]].
 * Then invert the image: [[1,1,0,0],[0,1,1,0],[0,0,0,1],[1,0,1,0]]
 * 
 * Notes:
 * 1 <= A.length = A[0].length <= 20
 * 0 <= A[i][j] <= 1
 */

public class FlippingAnImage832 {
    public int[][] flipAndInvertImage(int[][] A) {
        int N = A.length;
        int[][] res = new int[N][N];
        for (int i=0; i<N; i++) {
            for (int j=0; j<N; j++) {
                res[i][j] = 1 - A[i][N - j-1];
            }
        }
        return res;
    }


    public int[][] flipAndInvertImage2(int[][] A) {
        for (int i=0; i<A.length; i++) {
            reverseAndFlip(A[i]);
        }
        return A;
    }
    
    private void reverseAndFlip(int[] row) {
        int lo = 0;
        int hi = row.length - 1;
        while (lo <= hi) {
            swapAndFlip(row, lo++, hi--);
        }
    }
    
    private void swapAndFlip(int[] row, int i, int j) {
        if (i == j) {
            row[i] = 1 - row[i];
            return;
        }
        int tmp = row[i];
        row[i] = 1 - row[j];
        row[j] = 1- tmp;
    }

}