二维数组

# 48. 旋转图像 (opens new window)

class Solution {
    public void rotate(int[][] matrix) {
        int m = matrix.length;
        for(int i=0;i<m;i++){
            for(int j=i;j<m;j++){
                int tmp = matrix[i][j];
                matrix[i][j] = matrix[j][i];
                matrix[j][i] = tmp;
            }
        }
        for(int[] row:matrix){
            reverseRow(row);
        }
    }
    void reverseRow(int[] arr){
        int i=0,j=arr.length-1;
        while(i<j){
            int tmp = arr[i];
            arr[i] = arr[j];
            arr[j] = tmp;
            i++;j--;
        }
    }
}

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# 54. 螺旋矩阵 (opens new window)

class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        int m = matrix.length;
        int n = matrix[0].length;
        int l=0,r=n-1;
        int u=0,b=m-1;
        List<Integer> ret = new ArrayList<>();
        while(ret.size()<m*n){
            if(u<=b){
                for(int i=l;i<=r;i++){
                    ret.add(matrix[u][i]);
                }
                u++;
            }
            if(l<=r){
                for(int j=u;j<=b;j++){
                    ret.add(matrix[j][r]);
                }
                r--;
            }
            if(b>=u){
                for(int i=r;i>=l;i--){
                    ret.add(matrix[b][i]);
                }
                b--;
            }
            if(r>=l){
                for(int j=b;j>=u;j--){
                    ret.add(matrix[j][l]);
                }
                l++;
            }
        }
        return ret;
    }
}

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# 73. 矩阵置零 (opens new window)

class Solution {
    public void setZeroes(int[][] matrix) {
        int m = matrix.length;
        int n = matrix[0].length;
        boolean[] row = new boolean[m];
        boolean[] col = new boolean[n];
        for(int i=0;i<m;i++){
            for(int j=0;j<n;j++){
                if(matrix[i][j]==0){
                    row[i] = col[j] = true;
                }
            }
        }
        for(int i=0;i<m;i++){
            for(int j=0;j<n;j++){
                if(row[i] || col[j]){
                    matrix[i][j] = 0;
                }
            }
        }
    }
}

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# 240. 搜索二维矩阵 II (opens new window)

class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        int m = matrix.length;
        int n = matrix[0].length;
        int i=0,j=n-1;
        while(i<m && j>=0){
            if(target==matrix[i][j]){
                return true;
            }else if(target<matrix[i][j]){
                j--;
            }else{
                i++;
            }
        }
        return false;
    }
}

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