最大子方阵

来源：互联网发布：丹尼斯约翰逊数据编辑：程序博客网时间：2024/06/02 18:35
package 最大子方阵;/** * Created by h on 16-12-18. */public class Solution {    public int maxSubMatrix(int[][] mat, int n) {        int[][] right = new int[n][n];        int[][] down = new int[n][n];        //时间复杂度O（n3）        int type = 1;        preProcess(mat, right, down, n, type);        int[] ans = new int[1];        ans[0] = 0;        dp(ans, right, down, n);        type = 0;        preProcess(mat, right, down, n, type);        dp(ans, right, down, n);        return ans[0];    }    private void dp(int[] ans, int[][] right, int[][] down, int n) {        for (int i = 0; i < n; i++) {            for (int j = 0; j < n; j++) {                int maxNum = Math.min(right[i][j], down[i][j]);                for (int k = maxNum; k > 0; k--) {                    if (down[i][j + k - 1] >= k && right[i + k - 1][j] >= k) {                        ans[0] = Math.max(k, ans[0]);                        break;                    }                }            }        }    }    private void preProcess(int[][] mat, int[][] right, int[][] down, int n, int type) {        for (int i = 0; i < n; i++) {            for (int j = 0; j < n; j++) {                right[i][j] = 0;                down[i][j] = 0;            }        }        for (int i = 0; i < n; i++) {            for (int j = 0; j < n; j++) {                for (int k = j; k < n; k++) {                    if (mat[i][k] == type) {                        right[i][j]++;                    } else {                        break;                    }                }                for (int k = i; k < n; k++) {                    if (mat[k][j] == type) {                        down[i][j]++;                    } else {                        break;                    }                }            }        }    }    public static void main(String[] args) {        int[][] mat = {                {0, 1, 1, 1, 1},                {0, 1, 0, 0, 1},                {0, 1, 0, 0, 1},                {0, 1, 1, 1, 1},                {0, 1, 0, 1, 1}        };        int n = mat.length;        System.out.println(new Solution().maxSubMatrix(mat, n));    }}
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