05 August 2008
行列均为非递增（降序），统计负数的总数量
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public int countNegatives(int[][] grid) {
int rows = grid.length, cols = grid[0].length;
int res = 0, lastNeg = cols - 1;
for (int row = 0; row < rows; row++) {
//check edge cases - if first element is < 0 - all elements in row are negative
if (grid[row][0] < 0) {
res+=cols;
continue;
}
//if last element is positive - it means there are no negative numbers in a row
if (grid[row][cols - 1] > 0)
continue;
//there is a mix of negative and positive ones, need to find the border. starting
//binary search
int l = 0, r = lastNeg;
while (l <= r) {
int m = l + (r - l)/2;
if (grid[row][m] < 0) {
r = m - 1;
} else
l = m + 1;
}
//l points to the first negative element, which means cols - l is a number of
//such elements
res += (cols - l); lastNeg = l;
}
return res;
}