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  • 【Spiral Matrix II】cpp

    题目:

    Given an integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.

    For example,
    Given n = 3,

    You should return the following matrix:

    [
     [ 1, 2, 3 ],
     [ 8, 9, 4 ],
     [ 7, 6, 5 ]
    ]

    代码:

    class Solution {
    public:
        vector<vector<int>> generateMatrix(int n) {
                vector<vector<int> > ret(n, vector<int>(n,0));
                int circle = n/2;
                int v = 1;
                for ( int c=0; c<circle; ++c )
                {
                    // up
                    for ( int col=c; col<n-c; ++col ) ret[c][col]=v++;
                    // right
                    for ( int row=c+1; row<n-c-1; ++row ) ret[row][n-1-c]=v++;
                    // down
                    for ( int col=n-1-c; col>=c; --col ) ret[n-1-c][col]=v++;
                    // left
                    for ( int row=n-2-c; row>c; --row) ret[row][c]=v++;
                }
                if ( n & 1 )
                {
                    ret[circle][circle]=v;
                }
                return ret;
        }
    };

    tips:

    按照Spiral Matrix的顺序走一遍元素,维护一个v每次运算后+1。

    ============================================

    第二次过这道题,思路跟第一次一样。

    class Solution {
    public:
        vector<vector<int>> generateMatrix(int n) {
                vector<vector<int> > ret(n, vector<int>(n,1));
                if ( n<1 ) return ret;
                int val = 1;
                for ( int i=0; i<n/2; ++i )
                {
                    // north
                    for ( int p=i; p<n-i; ++p ) ret[i][p] = val++; 
                    // east
                    for ( int p=i+1; p<n-1-i; ++p ) ret[p][n-1-i] = val++;
                    // south
                    for ( int p=i; p<n-i; ++p ) ret[n-1-i][n-1-p] = val++;
                    // west
                    for ( int p=i+1; p<n-1-i; ++p ) ret[n-1-p][i] = val++;
                }
                if ( n & 1 ) ret[n/2][n/2] = val;
                return ret;
        }
    };
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  • 原文地址:https://www.cnblogs.com/xbf9xbf/p/4562464.html
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