leetcode 1337

Constraints:

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1. m == mat.length
2. n == mat[i].length
3. 2 <= n, m <= 100
4. 1 <= k <= m
5. matrix[i][j] is either 0 or 1.

我写的，这个时候并没有用PriorityQueue. arr是加上位置权重之后的一维数组，a是K个数排序之后的数组，num是K个数对应的index数组，两个tmp是在用交换的方式排序.

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class Solution {
    public int[] kWeakestRows(int[][] mat, int k) {
        int m = mat.length, n = mat[0].length;
        double[] arr = new double[m];
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                arr[i] += mat[i][j];
            }
            arr[i] += 0.01*i;
        }
        
        // a: after sorting; num: index
        double[] a = new double[k];
        int[] nums = new int[m];
        for (int i = 0; i < m; ++i) {
            nums[i] = i;
        }
        for (int i = 0; i < k; ++i) {
            int index = i;
            for (int j = i; j < m; ++j) {
                if (arr[index] > arr[j]) {
                    index = j;
                }
            }
            a[i] = arr[index];
            
            double tmp1 = arr[i];
            arr[i] = arr[index];
            arr[index] = tmp1;
            
            int tmp2 = nums[i];
            nums[i] = nums[index];
            nums[index] = tmp2;
        }
        
        int[] num_k = new int[k];
        System.arraycopy(nums, 0, num_k, 0, k);
        return num_k;
    }
}

System.arraycopy是为了返回新创建的数组，用法详情见另一篇。